Laser selective melting forming method of light rare earth strengthened aluminum magnesium alloy impeller

Abstract

The application discloses a laser selective melting forming method of a rare earth reinforced light-weight aluminum magnesium alloy impeller, and comprises the following steps: establishing a three-dimensional model of the impeller; determining a forming direction of the impeller; presetting a shrinkage amount of the three-dimensional model according to an outer diameter of the impeller; adding support to the three-dimensional model according to the forming direction of the impeller; performing laser selective melting forming according to the preset shrinkage amount and the three-dimensional model after the support is added, so as to obtain the impeller with a substrate and support; performing reinforced heat treatment on the impeller with the substrate and support; and removing the substrate and support of the impeller, so as to obtain the impeller. The application has a short preparation period and can obtain a high-strength impeller with excellent strength and elongation.

Description

TECHNICAL FIELD

[0001] The application relates to a laser selective melting forming method of a rare earth reinforced light aluminum magnesium alloy impeller, and belongs to the technical field of metal additive manufacturing. BACKGROUND

[0002] A turbine oxygen pump impeller is an important component of a liquid rocket engine, and guarantees efficient, reliable and continuous supply of oxidant during engine operation. The impeller is mostly of a closed structure, and has a large number of blades and a complex profile, which is prone to tool interference, and cannot be directly machined to form the whole flow passage. At present, the impeller is mainly formed by precision casting, but internal quality control is difficult, and defects such as composition segregation, shrinkage, shrinkage, cracks, insufficient pouring and the like are prone to occur, the product qualified rate is low, the production cycle is long, and the cost is high.

[0003] The laser selective melting forming technology can form a product prototype or a part according to a three-dimensional model of the part, is not limited by the structure of the part, has a short manufacturing cycle and a high product qualified rate, and is very suitable for the whole rapid manufacturing of the impeller. However, since the working pressure of a new generation of liquid oxygen kerosene engine turbine oxygen pump impeller is much higher than that of a conventional carrier engine, the tensile strength of the impeller material is required to be not less than 500 MPa, and the tensile strength of the most widely used laser selective melting forming aluminum silicon alloy material is only 290 MPa, and the elongation is only 2%, which cannot meet the performance requirements of the engine. Therefore, the whole rapid manufacturing of the high-strength light alloy impeller has become a big problem in the field of engine manufacturing. SUMMARY

[0004] The application aims at overcoming the above-mentioned defects, and provides a laser selective melting forming method of a rare earth reinforced light aluminum magnesium alloy impeller, which solves the technical problems of low strength and large weight of the existing laser selective melting forming impeller, has a short preparation cycle, and can obtain a high-strength impeller with excellent strength and elongation.

[0005] In order to achieve the above-mentioned application purposes, the application provides the following technical scheme.

[0006] The application provides a laser selective melting forming method for a large-size impeller of a rare earth reinforced light aluminum magnesium alloy, and belongs to the technical field of metal additive manufacturing.

[0007] The application provides a laser selective melting forming method for a large-size impeller of a rare earth reinforced light aluminum magnesium alloy, and belongs to the technical field of metal additive manufacturing.

[0008] A three-dimensional model of the impeller is established.

[0009] The forming direction of the impeller is determined.

[0010] A preset shrinkage amount is preset for the three-dimensional model according to the outer diameter of the impeller; and supports are added to the three-dimensional model.

[0011] The laser selective melting forming is performed according to the three-dimensional model after the preset shrinkage amount and the supports are added, so that the impeller with the substrate and the supports is obtained.

[0012] The impeller with the substrate and the supports is subjected to a strengthening heat treatment.

[0013] The substrate and the supports of the impeller are removed, so that the impeller is obtained.

[0014] Further, the impeller comprises an upper convex shoulder, a lower convex shoulder, a curved cover plate, a flat cover plate and blades located between the curved cover plate and the flat cover plate.

[0015] The forming direction of the impeller is determined as the curved cover plate downward, and the central axis of the impeller is placed at an angle of 40-45 degrees with the horizontal plane.

[0016] Further, the method for presetting the shrinkage amount for the three-dimensional model according to the outer diameter of the impeller comprises the following steps.

[0017] When the outer diameter of the impeller is greater than 250 mm, 0.4-0.5% shrinkage amount is preset in the X and Y directions, and 0.2% shrinkage amount is preset in the Z direction; when the outer diameter of the impeller is less than or equal to 250 mm, 0.2-0.3% shrinkage amount is preset in the X and Y directions, and 0.1% shrinkage amount is preset in the Z direction.

[0018] Wherein, the Z direction is vertical direction, and the plane where the X and Y directions are located is horizontal plane.

[0019] Further, the method for adding support to the three-dimensional model comprises:

[0020] For the circumferential outlet position in the three-dimensional model, add a whole-circle solid support with a thickness of 1.5mm-3mm;

[0021] For the curved cover plate outer circle and end face in the three-dimensional model, add a solid support with a thickness of ≥3mm;

[0022] For the upper shoulder end face in the three-dimensional model, add a solid support with a thickness of ≥3mm;

[0023] For the blade in the three-dimensional model, add a grid support to the part with an angle less than 45° with the horizontal plane, and do not add support to the part with an angle not less than 45° with the horizontal plane.

[0024] Further, the laser selective melting forming is performed by using a rare earth reinforced light aluminum magnesium alloy as the forming material;

[0025] The aluminum magnesium alloy comprises the following components by mass percentage:

[0026] Mg: 6.0%-9.0%;

[0027] Sc: 0.5%-1.0%;

[0028] Zr: 0.2%-0.7%;

[0029] Al: balance.

[0030] Further, the parameters for the laser selective melting forming comprise:

[0031] The laser selective melting forming parameters for the impeller and the solid support are: laser power 340-380W, scanning speed 1000-1300mm / s, scanning interval 0.10-0.12mm, powder layer thickness 0.03mm, and phase angle 67°; the laser selective melting forming parameters for the grid support are: laser power 180-220W, scanning speed 1000-1300mm / s, scanning interval 0.10-0.12mm, powder layer thickness 0.03-0.06mm, and phase angle 67°.

[0032] Further, the method for strengthening heat treatment of the impeller with the substrate and the support comprises:

[0033] After being kept at 300-350℃ for 4-8h, air cooling is performed.

[0034] Further, the forming method further comprises:

[0035] After removing the base plate and support carried by the impeller, the inside of the impeller is polished by using the abrasive flow;

[0036] The polishing method comprises rough grinding and fine grinding, the rough grinding selects medium hardness abrasive, the grit size is 100 mesh, the grinding pressure is 4-5 MPa, and the processing time is 20-40 min; the fine grinding selects soft abrasive, the grit size is 400 mesh, the grinding pressure is 3.5-4.5 MPa, and the processing time is 40-60 min.

[0037] Further, a three-dimensional model of the impeller is established by using UG or Pro / E, and is exported in STL format, and the export accuracy is not less than 0.008 mm.

[0038] Further, the tensile strength of the obtained impeller is not less than 500 MPa, and the elongation rate is not less than 12%.

[0039] Compared with the prior art, the present application has at least one of the following beneficial effects:

[0040] (1) The present application creatively adopts laser selective melting to integrally form the impeller, does not need to design a mold, and only needs to directly additively manufacture the part through the three-dimensional model of the impeller, so that short-period rapid manufacturing of the impeller is realized. The product quality is stable, the qualified rate is high, the organizational structure is dense, the grain is small, and the mechanical properties are excellent.

[0041] (2) The material used in the impeller of the present application is a rare earth strengthened light aluminum magnesium alloy, and after heat treatment, the tensile strength is not less than 500 MPa, and the elongation rate is not less than 12%. Compared with the laser selective melting forming of aluminum silicon alloy material, the overall performance of the laser selective melting forming of aluminum magnesium alloy closed impeller is improved, the strength is improved by 73%, and the elongation rate is improved by 300%.

[0042] (3) The present application guarantees the dimensional accuracy and surface roughness of the large-size impeller (diameter exceeding 250 mm) through pre-shrinking and abrasive flow treatment, the accuracy can reach ±0.1 mm, and the surface roughness after polishing can reach Ra1.6 μm. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 Fig. 1 is a schematic diagram of a closed impeller structure, wherein (a) is a front view, and (b) is a sectional view;

[0044] Figure 2 Fig. 2 is a schematic diagram of a closed impeller forming scheme;

[0045] Figure 3 Fig. 3 is a flow chart of the laser selective melting forming method of the rare earth strengthened light aluminum magnesium alloy impeller of the present application. DETAILED DESCRIPTION

[0046] The features and advantages of the present application will become more apparent from the detailed description set forth below.

[0047] The term "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any implementation described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other implementations. The description set forth herein, in connection with the appended drawings, describes and discloses various aspects of the embodiments. Unless otherwise noted, the drawings are not drawn to scale.

[0048] The present application provides a laser selective melting forming method of a rare earth strengthened light-weight aluminum-magnesium alloy impeller, the steps of the method comprising:

[0049] (1) establishing a three-dimensional model of the impeller;

[0050] (2) determining the forming direction of the three-dimensional model of the impeller established in step (1);

[0051] (3) reasonably pre-scaling the three-dimensional model of the impeller according to the outer diameter of the impeller and the forming direction determined in step (2) and adding supports;

[0052] (4) slicing the three-dimensional model of the impeller determined in step (3), and inputting the laser selective melting forming process parameters of the rare earth strengthened light-weight aluminum-magnesium alloy material to obtain a processing program file;

[0053] (5) performing laser selective melting forming according to the processing program file obtained in step (4) in an inert atmosphere to obtain the impeller with a substrate and supports, and cleaning the floating powder on the surface of the impeller;

[0054] (6) performing strengthening heat treatment on the impeller with the substrate and supports obtained in step (5);

[0055] (7) removing the substrate and supports of the impeller after the heat treatment in step (6);

[0056] (8) performing surface finishing on the impeller after removing the substrate and supports in step (7) to obtain a high-strength light-weight closed impeller.

[0057] In one specific embodiment, the impeller is composed of an upper cover plate, a lower cover plate and blades, the blades are located between the upper and lower cover plates, and the hub diameter of the impeller exceeds 250 mm. After heat treatment, the tensile strength of the rare earth strengthened light-weight aluminum-magnesium alloy impeller is not less than 500 MPa, and the elongation rate is not less than 12%.

[0058] In one specific embodiment, in step (1), a modeling software such as UG or Pro / E is used to establish the three-dimensional model of the impeller, and the model is exported in STL format with an accuracy of not less than 0.008 mm.

[0059] In one specific embodiment, in step (2), the impeller three-dimensional model is placed with the upper cover plate facing down and the impeller central axis at an angle of 40° with the horizontal direction.

[0060] In one specific embodiment, in step (3), the impeller three-dimensional model is reasonably pre-scaled, and the pre-scaling amount is regularly 0.4-0.5% in the X and Y directions and 0.2% in the Z direction when the impeller outer diameter is greater than 250 mm, and 0.2-0.3% in the X and Y directions and 0.1% in the Z direction when the impeller outer diameter is less than or equal to 250 mm.

[0061] In one specific embodiment, in step (3), in the magics software, a whole-circle solid support with a thickness of 1.5-3 mm is added to the circumferential outlet position in the three-dimensional model; a deformation-preventing solid support with a thickness of greater than or equal to 3 mm is added to the outer circle and end face of the curved cover plate; a deformation-preventing solid support with a thickness of greater than or equal to 3 mm is added to the upper convex shoulder end face; and a grid support is added to the part of the blade with an angle less than 45° with the horizontal plane.

[0062] In one specific embodiment, in step (4), a rare-earth strengthened light aluminum magnesium alloy is used as the forming material, and the laser selective melting forming parameters of the impeller and the solid support are as follows: laser power 340-380 W, scanning speed 1000-1300 mm / s, scanning interval 0.10-0.12 mm, powder layer thickness 0.03 mm, and phase angle 67°; and the laser selective melting forming parameters of the grid support are as follows: laser power 180-220 W, scanning speed 1000-1300 mm / s, scanning interval 0.10-0.12 mm, powder layer thickness 0.03-0.06 mm, and phase angle 67°.

[0063] In one specific embodiment, in step (6), the heat treatment system is 300-350℃ for 4-8 h, and air cooling is performed.

[0064] In one specific embodiment, in step (8), abrasive flow is used for finishing the inside of the impeller, medium-hardness abrasives are selected for rough grinding, the abrasive particle size is 100 mesh, the grinding pressure is 4.5 MPa, and the processing time is 30 min; soft abrasives are selected for fine grinding, the abrasive particle size is 400 mesh, the grinding pressure is 4 MPa, and the processing time is 50 min.

[0065] The rare-earth strengthened light aluminum magnesium alloy used in the application has a tensile strength of not less than 500 MPa and an elongation of not less than 12% after heat treatment.

[0066] The application provides a laser selective melting forming method for a large-size impeller of a rare earth reinforced light aluminum magnesium alloy, and high-quality, high-strength and short-period rapid manufacturing of the impeller can be realized, the weight of the impeller is effectively reduced, and new requirements of light weight and integration in the field of aerospace are met.

[0067] Embodiment 1

[0068] The embodiment provides a laser selective melting forming method for a large-size impeller of a rare earth reinforced light aluminum magnesium alloy, and specific steps are as shown in the figure and include: Figure 3

[0069] (1) a three-dimensional model of the impeller is established by using modeling software such as UG or Pro / E, as shown in the figure, the diameter is 255 mm, the height is 90 mm, the outlet gap is 15 mm, there are 10 long blades between the upper and lower cover plates, the blade thickness is less than 3 mm, and the STL format is exported, and the export precision is not less than 0.008 mm. Figure 1

[0070] (2) the forming direction of the impeller is determined, as shown in the figure, the upper cover plate of the three-dimensional model of the impeller is placed downward at an angle of 40° with the horizontal direction. Figure 2

[0071] (3) 0.4% shrinkage is preset in the X and Y directions of the three-dimensional model of the impeller, 0.2% shrinkage is preset in the Z direction, the lower surface of the blade with an angle less than 30° with the horizontal direction is added with grid supports for easy removal, and the cover plate part of the impeller with an angle less than 40° with the horizontal direction is added with entity supports with high strength to prevent deformation.

[0072] (4) the three-dimensional model with the added supports is subjected to slicing treatment, and is placed into the laser selective melting forming parameters of the rare earth reinforced light aluminum magnesium alloy, the laser selective melting forming parameters of the impeller and the entity supports are as follows: laser power 340-380 W, scanning speed 1000-1300 mm / s, scanning interval 0.10-0.12 mm, powder layer thickness 0.03 mm, and phase angle 67°; the laser selective melting forming parameters of the grid supports are as follows: laser power 180-220 W, scanning speed 1000-1300 mm / s, scanning interval 0.10-0.12 mm, powder layer thickness 0.03-0.06 mm, and phase angle 67°, and the obtained machining program file is imported into the laser selective melting forming equipment.

[0073] (5) the forming cabin door of the laser selective melting forming equipment is closed, argon is introduced into the inside of the equipment, when the oxygen content in the forming cabin is less than 500 ppm, laser selective melting forming is started, argon supply should be maintained during the forming process to ensure that the oxygen content in the forming cabin is less than 500 ppm. After the forming is completed, the impeller with the substrate and the supports is taken out and the floating powder on the surface of the impeller is cleaned after the part is cooled for more than 4 hours.​​​

[0074] (6) Strengthening heat treatment of the impeller with the substrate and support, heat treatment system is 300-350 DEG C for 4-8h, air cooling.

[0075] (7) High-speed reciprocating wire electro-discharge wire cutting is used to remove the substrate, turning is used to remove the external support of the impeller, and manual polishing is used to remove the internal grid support of the impeller.

[0076] (8) Abrasive flow is used to finish the internal impeller, medium hardness abrasive is selected for rough grinding, the mesh number of abrasive particles is 100, the grinding pressure is 4.5MPa, and the processing time is 30min; soft abrasive is selected for fine grinding, the mesh number of abrasive particles is 400, the grinding pressure is 4MPa, and the processing time is 50min.

[0077] The present application is described in detail above in combination with specific embodiments and exemplary examples, but these descriptions cannot be understood as limitations of the present application. Those skilled in the art understand that the technical solutions and embodiments of the present application can be variously replaced, modified or improved without departing from the spirit and scope of the present application, and these all fall within the scope of the present application. The protection scope of the present application is subject to the appended claims.

[0078] The contents not described in detail in the specification of the present application are the known technology of those skilled in the art.

Claims

1. A method for laser selective melting forming of a light rare earth strengthened aluminum magnesium alloy impeller, characterized in that, The method comprises the following steps: establishing a three-dimensional model of the impeller; determining the forming direction of the impeller; presetting a shrinkage amount for the three-dimensional model according to the outer diameter of the impeller; adding supports to the three-dimensional model; forming the impeller with the substrate and the supports by laser selective melting according to the preset shrinkage amount and the three-dimensional model with the added supports; performing a strengthening heat treatment on the impeller with the substrate and the supports; removing the substrate and the supports from the impeller to obtain the impeller; the impeller comprises an upper convex shoulder (1), a lower convex shoulder (2), a curved cover plate (3), a flat cover plate (4) and blades (5) between the curved cover plate (3) and the flat cover plate (4); the forming direction of the impeller is determined as the curved cover plate (3) downward, and the central axis of the impeller is placed at an angle of 40°-45° with the horizontal plane; the method for presetting a shrinkage amount for the three-dimensional model according to the outer diameter of the impeller comprises the following steps: when the outer diameter of the impeller is greater than 250 mm, presetting a shrinkage amount of 0.4-0.5% in the X and Y directions and a shrinkage amount of 0.2% in the Z direction; and when the outer diameter of the impeller is less than or equal to 250 mm, presetting a shrinkage amount of 0.2-0.3% in the X and Y directions and a shrinkage amount of 0.1% in the Z direction; wherein the Z direction is the vertical direction, and the X and Y directions are in the horizontal plane; the method for adding supports to the three-dimensional model comprises the following steps: adding a whole-circle solid support with a thickness of 1.5-3 mm to the circumferential outlet position in the three-dimensional model; adding a solid support with a thickness of greater than or equal to 3 mm to the outer circle and the end face of the curved cover plate (3) in the three-dimensional model; adding a solid support with a thickness of greater than or equal to 3 mm to the end face of the upper convex shoulder (1) in the three-dimensional model; adding a grid support to the part of the blades (5) in the three-dimensional model with an angle less than 45° with the horizontal plane, and not adding supports to the part of the blades (5) in the three-dimensional model with an angle not less than 45° with the horizontal plane.

2. The method according to claim 1, wherein the method is characterized by, The laser selective melting is performed by using a rare earth strengthened light aluminum magnesium alloy as a forming material; the aluminum magnesium alloy comprises the following components by mass percentage: Mg: 6.0%-9.0%; Sc: 0.5%-1.0%; Zr：0.2％～0.7％； Al: the balance.

3. The method according to claim 2, wherein the method is characterized by, The parameters for the laser selective melting comprise: the laser selective melting parameters for the impeller and the solid support are as follows: laser power 340-380 W, scanning speed 1000-1300 mm / s, scanning interval 0.10-0.12 mm, powder layer thickness 0.03 mm, and phase angle 67°; and the laser selective melting parameters for the grid support are as follows: laser power 180-220 W, scanning speed 1000-1300 mm / s, scanning interval 0.10-0.12 mm, powder layer thickness 0.03-0.06 mm, and phase angle 67°.

4. The method according to claim 1, wherein the method is characterized by, The method for performing a strengthening heat treatment on the impeller with the substrate and the supports comprises the following steps: performing air cooling after being kept at 300-350 ℃ for 4-8 h.

5. The method of claim 1, wherein the method further comprises: The method further comprises the following steps: after the substrate and the supports are removed from the impeller, performing a finishing treatment on the inside of the impeller by using abrasive flow; the finishing treatment method comprises coarse grinding and fine grinding, the coarse grinding uses medium-hardness abrasive, the abrasive grain size is 100 mesh, the grinding pressure is 4-5 MPa, and the processing time is 20-40 min; and the fine grinding uses soft abrasive, the abrasive grain size is 400 mesh, the grinding pressure is 3.5-4.5 MPa, and the processing time is 40-60 min.

6. The method of claim 1, wherein the method further comprises: The three-dimensional model of the impeller is established by using UG or Pro / E and is exported in STL format, and the exporting precision is not less than 0.008 mm.

7. The method according to claim 1, wherein the method is characterized by, The obtained impeller has tensile strength not less than 500 MPa and elongation not less than 12%.

Images