Electron beam selective melting forming method for TiAl alloy swirler with complex structure

Abstract

The invention provides an electron beam selective melting forming method for a TiAl alloy swirler of a complex structure. The electron beam selective melting forming method specifically comprises the steps that firstly, a blank model is made; 2, placing parts and adding supports; 3, forming process; 4, performing a post-treatment process; and after forming is finished, the swirler part is taken out of the forming cavity of the forming equipment. The method comprises the steps that firstly, powder cleaning is conducted on parts, and residual electron beam selective melting TiAl alloy powder is recycled and reused through a PRS system; secondly, performing heat treatment on the part to optimize the performance of the part; machining the mounting edge of the part; and finally, an abrasive flow process is carried out for the interiors of cavities, blades and the like of the parts, and a sand blowing process is carried out on the outer surfaces of the parts. The method has the advantages that the electron beam selective melting forming preparation of the TiAl alloy swirler part with the complex structure is realized through the whole set of process development, mainly including the forming process of the interior and the outline, the support setting and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal additive manufacturing, in particular to an electron beam selective melting forming method of a complex structure TiAl alloy vortex finder. BACKGROUND

[0002] The vortex finder has a whole body of revolution structure, and the inner cavities are uniformly distributed with reverse double-stage blades, and the part is located at the head of the flame tube. The vortex finder part has the following functions in the aero-engine: 1. forming a low-pressure backflow area to stabilize the flame at the head of the flame tube; 2. generating vortex air in the combustion chamber to achieve the purpose of full combustion of fuel by mixing fuel and air.

[0003] The traditional vortex finder is made of high-temperature alloy. In order to improve the comprehensive performance of the aero-engine, part weight reduction is one of the important ways, and if TiAl alloy is used to replace high-temperature alloy, the part can be reduced by more than 50%, which has great weight reduction benefit.

[0004] TiAl alloy (TiAl intermetallic compound) is a new lightweight alloy researched at home and abroad. The alloy has the characteristics of low density (3.9-4.2 g / cm 3 , high strength, high modulus, good creep resistance and high-temperature gas corrosion resistance, and the long-term use temperature can reach 750 DEG C. It can be used as a turbine blade, a vortex finder and other parts, and can partially replace nickel-based high-temperature alloy structural materials, greatly reduce the structure weight, improve the engine performance, and has a wide application prospect in the field of aviation, aerospace and high-speed aircraft.

[0005] Due to the poor processing performance of TiAl alloy and other reasons, the traditional forming process is difficult to prepare TiAl alloy parts with good metallurgical quality and comprehensive performance. In the precision casting process, the violent reaction between the TiAl alloy melt and the surface of the mold shell causes pollution, the excessive growth of alpha phase in the single-phase region, and the segregation of Nb element, which will deteriorate the room temperature plasticity of TiAl alloy; in the isothermal forging process, the beta phase which is beneficial to high-temperature deformation cannot be preserved at room temperature, and the B2 phase formed will seriously deteriorate the room temperature plasticity; in the powder metallurgy process, it is difficult to control the oxygen content, and if the oxygen content exceeds 1000 ppm, the room temperature plasticity will be greatly reduced. The traditional TiAl alloy forming process technology is difficult to break through, which limits the large-scale application of TiAl alloy.

[0006] Electron beam selective melting (EBM) is used for TiAl alloy forming due to its unique advantages, and becomes a current research hotspot. EBM technology uses high-energy density, fast-moving electron beam as heat source, and maintains the forming temperature above 900 DEG C through preheating, which can effectively prevent TiAl alloy from fast cooling below the ductile-brittle transition temperature, and the micro-zone metallurgical process can effectively reduce the grain size and inhibit the micro-segregation. Meanwhile, the preparation process can effectively avoid the pollution of the mold shell due to the non-use of the mold, thereby improving the room temperature plasticity of TiAl alloy and providing the possibility for the forming of high-performance TiAl alloy parts. SUMMARY

[0007] The present application adopts electron beam selective melting forming technology to prepare TiAl alloy vortex generator parts, which makes up for the shortcomings of traditional manufacturing process, and has certain advantages for difficult-to-process alloys and complex structure parts formed by traditional process. The present application fully considers the forming process of TiAl vortex generator parts, ensures the internal density and the surface smoothness of the contour, and also carries out support design of part forming, which facilitates the removal in the later stage while ensuring the part forming.

[0008] The present application provides an electron beam selective melting forming method suitable for complex structure TiAl alloy vortex generator, fully considers the forming process of TiAl vortex generator parts, ensures the internal density and the surface smoothness of the contour, and also carries out support design of part forming, which facilitates the removal in the later stage while ensuring the part forming.

[0009] The present application provides an electron beam selective melting forming method of complex structure TiAl alloy vortex generator, specifically comprising: I. Blank model making According to the design requirements, the upper and lower surfaces of the mounting edge need to be assembled with other parts, and the surface roughness requirement is Ra1.6. Laser selective melting forming cannot guarantee the surface roughness, so a certain amount of allowance is reserved on the upper and lower surfaces of the mounting edge, and the surface roughness is improved by machining the mounting edge allowance in the later stage.

[0010] II. Part placement and support addition When the outlet end of the convergent section of the vortex finder part is placed vertically downward, there is a large area of suspended surface inside the cavity, and the height distance is large, so support needs to be added, and the support penetrates into the part with a deep distance, and the support removal and support surface polishing are relatively difficult. When the outlet end of the convergent section of the vortex finder part is placed vertically upward, the blades inside the part form an angle of 45°-65° with the horizontal direction, which is greater than 45° to achieve self-forming, at this time the inner ring channel edge, outer ring channel edge, inner ring blade edge and outer ring blade edge of the vortex finder need to be added support, but the support height is small, and it is simple to remove later, so this placement method is feasible. Since the electron beam selective melting technology is used to form TiAl alloy, in order to prevent the "blowing powder" phenomenon from occurring during forming, a preheating scan needs to be performed first. Before melting each layer of powder, under the premise of ensuring that the powder layer does not collapse, a large beam focus electron beam is used to quickly scan the powder layer to make the powder slightly sintered to obtain sufficient impact resistance, and then selective melting is performed. At this time, the slightly sintered powder has a certain supporting effect, but in order to ensure stable forming of the part, a certain amount of support needs to be set to cooperate with the slightly sintered powder to complete the preparation of the part. At the part mounting edge, a thin-walled contour support is used, and the support thickness is 0.2-0.5mm. The contour support is inclined and connected with the substrate to avoid being placed vertically and directly connected with the outer surface of the part. A plurality of layers of thin-walled contour supports are generated from inside to outside in the area below the mounting edge, and the contour support is in contact with the lower surface of the mounting edge of the vortex finder. The contact part is sawtooth-shaped and is inserted into the part by 0.1mm, which is convenient for removal while ensuring firm connection. In order to more conveniently remove the contour support of the mounting edge, the thin-walled contour support device is in a hollow structure, which further weakens its strength. A thin-walled contour support is also used on the outer ring surface of the vortex finder inlet, and the support thickness is 0.2-0.5mm. The support is vertically connected with the substrate. A plurality of layers of thin-walled contour supports are generated from inside to outside on the outer ring surface, and the contour support is in contact with the lower surface of the mounting edge of the vortex finder. The contact part is sawtooth-shaped and is inserted into the part by 0.1mm, which is convenient for removal while ensuring firm connection. Crossed plate supports are added at the suspended position of the blade head of the vortex finder, and the support thickness is 0.2-0.5mm, which ensures that the support grows stably perpendicular to the substrate and does not warp.

[0011] III. Forming process During the forming of the part, the part scanning path is to scan the inner core first and then scan the outer contour; the contour support and the line support only scan the inner core. Through the above scanning mode, the forming precision and forming efficiency of the part are ensured, and the support is also easier to remove, thereby improving the manufacturing efficiency. In the height direction of the vortex finder part, due to the difference in the circumference of the profile cross section in different height directions, different numbers of beam splitting are selected to set, and through the outer layer small beam flow + the next outer layer large beam flow, the contour smoothness is ensured while the surface density is improved.

[0012] The application provides a laser selective melting forming scheme of a complex structure TiAl alloy vortex flow device, cooperates with corresponding placement modes, support settings, process parameter regulation and the like, guarantees the requirements of part surface smoothness and internal organization density, and facilitates the removal of the support.

[0013] IV. Post-processing technology After the forming is completed, the vortex flow device part is taken out from the forming cavity of the forming equipment. First, the part is subjected to powder cleaning, and residual electron beam selective melting TiAl alloy powder is recycled and reused through the PRS system; second, the part is subjected to heat treatment, and the performance of the part is optimized; the mounting edge of the part is machined; finally, the internal cavities, blades and the like of the part are subjected to the abrasive flow process, and the outer surface of the part is subjected to the sandblasting process.

[0014] Advantages of the application: Through the whole set of process development, mainly including the forming process of the internal and contour and the support setting and the like, the electron beam selective melting forming preparation of the complex structure TiAl alloy vortex flow device part is realized. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 : schematic view of a vortex flow device part; Figure 2 : schematic view of vortex flow device part excess addition; Figure 3 : front view of vortex flow device support addition; Figure 4 : bottom view of vortex flow device support addition; Figure 5 : schematic view of vortex flow device part contour parameter setting area. DETAILED DESCRIPTION

[0016] The application will be further explained in conjunction with specific implementation schemes, but is not limited to the application, the structure, proportion, size and the like shown in the drawings of the specification are only used to cooperate with the content disclosed in the specification, for understanding and reading by those skilled in the art, and are not used to limit the limiting conditions of the implementation of the application, so they do not have technical substantive significance, any modification of the structure, change of the proportion relationship or adjustment of the size, without affecting the effects and purposes that can be achieved by the application, should still fall within the scope of the technical content disclosed by the application.

[0017] As shown in Figure 1 , the vortex flow device as a whole has a rotary body structure, the part has an inner ring channel and an outer ring channel, the inside of the channel is an inner ring blade and an outer ring blade, the middle of the part is a mounting edge, and the bottom of the part is a convergent section outlet.

[0018] Step one: three-dimensional modeling of the vortex generator was performed using modeling software, and the upper and lower surfaces of the installation edge were stretched by 1 mm, i.e. the installation edge of the part was thickened by 2 mm, as shown in Figure 2 .

[0019] Step two: the part model was imported into the model processing software for support addition.

[0020] The part was manufactured by using electron beam selective melting forming technology, and the part placement mode and overall support addition scheme are shown in Figures 3-4 , the outlet end of the convergent section of the vortex generator is placed vertically upward, and the installation edge, the outer edge of the inlet, the inner ring blade edge and the outer ring blade edge of the vortex generator are added with supports. At the installation edge of the part, a thin-walled contour support with a thickness of 0.3 mm is used. The contour support is inclined to the substrate, avoiding being set vertically and directly connected to the outer surface of the part. Four layers of thin-walled contour supports are generated from inside to outside in the area of the lower surface of the installation edge, and the contact between the contour support and the lower surface of the installation edge of the vortex generator is zigzag, which is inserted into the part by 0.1 mm, which is convenient for removal while ensuring firm connection. In order to remove the contour support of the installation edge more conveniently, the thin-walled contour support is set to a hollow structure, further weakening its strength. A thin-walled contour support with a thickness of 0.3 mm is also used on the outer ring surface of the vortex generator inlet, which is vertically connected to the substrate. Multiple layers of thin-walled contour supports are generated from inside to outside on the outer ring surface, and the contact between the contour support and the lower surface of the installation edge of the vortex generator is zigzag, which is inserted into the part by 0.1 mm, which is convenient for removal while ensuring firm connection. Crossed plate supports are added at the suspended position of the blade head of the vortex generator, with a thickness of 0.3 mm, which ensures that the support grows stably perpendicular to the substrate and does not warp.

[0021] Step three: the vortex generator model with added support is sliced and filled using software, specific process parameters are set, and a.cli format processing file is generated.

[0022] The substrate was preheated at a temperature of 1050°C for 30 minutes. The powder single-layer thickness was 0.5 mm, and after the powder was laid, the preheating process was as follows: electron beam current 8 mA, scanning speed 2 m / s, scanning times 10. After preheating, the melting forming was started, and the melting process was as follows: electron beam current 6 mA, scanning speed 0.8 m / s, melting times 2. After melting, energy compensation was performed again using the preheating process, and the powder was continuously laid for the next layer of forming.

[0023] In the part forming process, the part scanning path is to scan the core first, and then scan the outer contour; the contour support and the line support only scan the core. Through the above scanning mode, the forming precision and forming efficiency of the part are ensured, and the support is also easier to remove, improving the manufacturing efficiency. In the height direction of the vortex part, due to the difference in the length of the profile cross section in different height directions, different beam splitting quantities are selected, and through the outer small beam flow + the next outer large beam flow, the contour smoothness is ensured, and the surface area density is also improved. The specific area is shown in Figure 5 , and the specific parameters are shown in Table 1: Step four: import the processing file in step three into the electron beam selective melting forming equipment to form the part.

[0024] Step five: remove the powder and support of the part, and the residual electron beam selective melting TiAl alloy powder is recycled and reused by the PRS system until the powder is completely cleaned.

[0025] Step six: heat treatment of the part, the heat treatment process is: 1310-1340℃ / 4h, air cooling + 900-930℃ / 8h, furnace cooling.

[0026] Step seven: machine the part mounting edge. Coarse machining spindle speed 300r / min, feed 0.1mm / r, cutting depth 0.3mm; fine machining spindle speed 300r / min, feed 0.1mm / r, cutting depth 0.1mm.

[0027] Step eight: abrasive flow machining of the part, the specific parameters are: abrasive volume 500inch 3 , pressure 6MPa, cycle 4 times.

[0028] Step nine: sandblasting treatment is performed on the outer surface of the part to further improve the surface smoothness.

[0029] The remaining matters of the present application are known technologies.

[0030] Although the embodiments of the present application have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and variations can be made to the embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A method of electron beam selective melting forming of a complex structure TiAl alloy vortex, characterized in that: Specifically includes: I. Blank model formulation According to the design requirements, the upper and lower surfaces of the mounting edge need to be assembled with other parts, and the surface roughness requirement is Ra1.

6. Laser selective melting forming cannot guarantee the surface roughness of the mounting edge. The upper and lower surfaces of the mounting edge are reserved a certain amount of margin, and the surface roughness is improved by machining the mounting edge margin later. II. Part placement and support addition When the vortex part convergent section outlet end is placed vertically downward, there is a large area of suspended surface inside the cavity, and the height distance is large, so support needs to be added. The support goes deep into the part, and the support removal and support surface polishing are relatively difficult. When the vortex part convergent section outlet end is placed vertically upward, the angle between the blade inside the vortex part and the horizontal direction is 45° to 65°, which is greater than 45° to realize self-forming. At this time, the inner ring channel edge, outer ring channel edge, inner ring blade edge and outer ring blade edge of the vortex need to be supported. Since the electron beam selective melting technology needs to be preheated and scanned when forming TiAl alloy, before melting each layer of powder, under the premise of ensuring that the powder layer does not collapse, a large beam focus electron beam is used to quickly scan the powder layer to make the powder slightly sintered to obtain sufficient impact strength, and then selective melting is carried out. In order to ensure stable forming of the part, a certain amount of support is set to complete the preparation of the part together with the slightly sintered powder. III. Forming process During the forming of the part, the scanning path of the part is to scan the inner core first, and then scan the outer contour; the contour support and line support only scan the inner core; in the height direction of the vortex part, due to the difference in the circumference of the contour section at different heights, different beam splitting quantities are selected to set, and through the combination of small beam flow and large beam flow, the contour smoothness is guaranteed, and the surface density is improved. IV. Post-processing technology After the forming is completed, the vortex part is taken out from the forming cavity of the forming equipment; first, the powder is cleaned, and the residual electron beam selective melting TiAl alloy powder is recycled and reused by the PRS system; second, the part is heat treated to optimize the performance of the part; the mounting edge of the part is machined; finally, the internal cavity and blade of the part are processed by abrasive flow technology, and the external surface of the part is processed by sandblasting technology.

2. The method of electron beam selective melting forming of a complex structure TiAl alloy vortex according to claim 1, characterized in that: In the step two, the part placement and the support addition, in order to ensure the stable forming of the part, a certain amount of support is matched with the slightly sintered powder to jointly complete the part preparation; at the part mounting edge, a thin-walled contour support is used, and the support thickness is 0.2-0.5 mm; the contour support is inclined and connected with the substrate, so as to avoid being vertically arranged and directly connected with the outer surface of the part; the multi-layer thin-walled contour support is generated from inside to outside in the area of the lower surface of the mounting edge, the contact part between the contour support and the lower surface of the mounting edge of the vortex flow device is sawtooth-shaped, and is inserted into the part by 0.1 mm; the thin-walled contour support equipment is a hollow structure, and the strength is further weakened; the thin-walled contour support is also used on the outer annular surface of the inlet of the vortex flow device, and the support thickness is 0.2-0.5 mm; the support is vertically connected with the substrate; the multi-layer thin-walled contour support is generated from inside to outside on the outer annular surface, the contact part between the contour support and the lower surface of the mounting edge of the vortex flow device is sawtooth-shaped, and is inserted into the part by 0.1 mm, so that the part is conveniently removed and the connection is firm; the cross-shaped plate support is added at the suspended position of the blade head of the vortex flow device, and the support thickness is 0.2-0.5 mm.

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