Stress deformation regulation and control method for preparing hot-end casing suspended structure through selective laser melting

Abstract

The invention discloses a stress deformation regulation and control method for preparing a hot-end casing suspended structure through selective laser melting. The method comprises the following steps that the bottom of a model suspended part is cut into a bottom layer, a transition layer and a solid layer; the bottom layer is sliced, and the scanning mode is set to be strip scanning; the transition layer is sliced, the scanning mode is set to be chessboard-shaped scanning, and re-melting is conducted layer by layer; and the entity printing parameters are adopted for the entity layer to complete preparation of the part. According to the method, the suspended structure can be formed under the support-free condition, stress deformation is reduced, and the size precision and surface quality of the suspended structure are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-energy beam metal additive manufacturing, and in particular relates to a method for controlling stress and deformation of a suspended structure of a hot end casing prepared by selective laser melting. Background Art

[0002] As the structure of aircraft engines develops towards integration, the shapes of some parts are becoming more and more complex. Selective laser melting technology (SLM) mainly uses laser scanning of the powder bed layer by layer, which has unique advantages in the preparation of complex parts. However, during the forming of suspended structures, due to the accumulation of high thermal stress, the suspended structures are prone to warping and deformation, affecting the precision and forming ability of the parts. At present, the preparation of suspended structures mainly involves adding auxiliary supports to improve the formability of suspended structures and control stress deformation. Among them, after the hot end casing is designed with integration, there are more suspended structures. During the forming process, a large number of supports are usually required to assist in forming, resulting in a long post-processing time for parts, reducing the production efficiency of parts and increasing component costs. Summary of the invention

[0003] The main purpose of the present invention is to provide a method for controlling stress and deformation of a suspended structure of a hot end casing prepared by selective laser melting. The method can control the deformation of the suspended structure under unsupported conditions, achieve high-precision forming of the suspended structure, reduce the amount of post-processing, and improve the production efficiency of parts.

[0004] To this end, the present invention provides a method for controlling stress and deformation of a hot end casing suspended structure prepared by selective laser melting, comprising the following steps: Step 1: Divide the bottom of the suspended part of the hot end casing model into a bottom layer, a transition layer and a solid layer from bottom to top; Step 2: Slice the bottom layer of the suspended part, set the scanning mode to strip scanning, and use the printing device to print the bottom layer; Step 3: Slice the transition layer of the suspended part, set the scanning mode to chessboard scanning, and set layer-by-layer remelting. The remelting scanning mode adopts strip scanning, and use the printing equipment to print the transition layer; Step 4: The solid layer of the suspended part and the rest of the hot end casing model are formed using solid process parameters, and the scanning method is strip scanning to complete the preparation of the hot end casing.

[0005] Specifically, the thickness of the bottom layer is 0.1-0.2 mm, and the thickness of the transition layer is 0.3-0.6 mm. The reason why the thickness of the bottom layer is set at 0.1-0.2 mm is that when the thickness is greater than 0.2 mm, it is easy to cause warping and deformation due to heat treatment during printing. If it is less than 0.1 mm, it cannot support the transition layer. The transition layer is the main part for realizing unsupported forming. If the thickness of the transition layer is too small, the suspended part may also warp when forming the solid layer. If the thickness is too large, it will cause the forming efficiency to decrease and the forming accuracy to deteriorate.

[0006] Specifically, when printing the bottom layer of the suspended part, the laser power is set to 200-230W and the scanning speed is set to 1200-1500mm / s. Within this parameter range, the forming accuracy of the bottom layer can be guaranteed and thermal stress deformation can be reduced, providing a good base for the subsequent transition layer printing. If a smaller power or a higher speed is used, the bottom layer will not be well formed and there will be a large number of pores. If a higher power or a lower speed is used, the thermal stress accumulation will be aggravated due to the high energy input, causing the bottom layer to have a large warping deformation.

[0007] Specifically, the laser power of the chessboard scanning is set to 280-290W, the scanning speed is set to 1200-1500mm / s, the chessboard vector number is 50-200, and the laser power and scanning speed consistent with the chessboard scanning are used for layer-by-layer remelting. Chessboard scanning can effectively reduce the accumulation of thermal stress in the material. In order to make the transition layer and the entity layer more closely combined, the same laser power as the entity layer is used, and the scanning speed is relatively more likely to affect the accumulation of thermal stress. When the speed is too high, the powder bed cannot be fully melted, forming more pores, and when the speed is too low, it will cause stress accumulation to increase and cause warping and deformation. The number of chessboard vectors affects both stress accumulation and surface morphology. When the number of vectors is low, the surface flatness will be greater, affecting the forming accuracy. When the number of vectors is high, it will cause local thermal stress accumulation to be greater and deformation will occur. Layer-by-layer remelting can smooth the rough surface formed by chessboard scanning, which is beneficial to the forming of subsequent layers.

[0008] Specifically, the physical process parameters are a laser power of 280-290 W and a scanning speed of 920-980 mm / s.

[0009] Specifically, the thickness of the bottom layer is 0.2mm, the thickness of the transition layer is 0.5mm, when the bottom layer of the suspended part is printed, the laser power is 220W, the scanning speed is 1400mm / s, the laser power of the physical process parameters is 285W, the scanning speed is 960mm / s, and when scanning in a checkerboard shape, the laser power is set to 285W, the number of checkerboard vectors is 100, and the scanning speed is 1300mm / s.

[0010] During printing, the present invention ingeniously prints the bottom of the suspended structure of the hot end casing model in layers, and matches each layer with special printing parameters to achieve the purpose of regulating the thermal stress distribution at the bottom of the suspended structure, effectively reducing the stress deformation of the suspended structure under unsupported conditions. Among them, the bottom layer serves as the supporting base of the suspended structure on the powder bed. By controlling the thickness of the bottom layer to 0.1-0.2mm, and setting the scanning mode to strip scanning, combined with special printing process parameters, the forming accuracy of the bottom layer can be guaranteed while reducing thermal stress deformation, providing a good base for the subsequent transition layer printing. The transition layer is the main part of regulating stress distribution and reducing thermal stress deformation. By setting the thickness of the transition layer to 0.3-0.6mm, and setting the scanning mode to chessboard scanning, and setting layer-by-layer remelting, plus a special printing system, the thermal stress accumulation in the material can be effectively reduced. Layer-by-layer remelting can flatten the rough surface formed by chessboard scanning, which is conducive to the formation of subsequent layers.

[0011] In summary, this application successfully prepares a hot-end casing with accuracy that meets the design requirements under unsupported conditions by printing the suspended structure of the hot-end casing model in layers and combining it with a special printing system, thereby greatly reducing the post-processing steps of the hot-end casing and improving the efficiency of component preparation. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0013] Figure 1 This is a process flow chart of the hot end casing suspended structure forming process of the present invention; Figure 2 This is a schematic diagram of the layered model of the suspended part of the hot end casing. DETAILED DESCRIPTION

[0014] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0015] See also Figure 1 A method for controlling stress and deformation of a hot end casing suspension structure prepared by selective laser melting, comprising the following steps: Step 1: Divide the bottom of the suspended part of the hot end casing model into three layers, namely the bottom layer, the transition layer and the solid layer. Figure 2 Among them, the bottom layer provides a metal base for the transition layer to form, so as to avoid the transition layer being formed directly on the powder bed and affecting the forming accuracy. The transition layer is the main part to achieve support-free forming.

[0016] The inventors further found that it is more appropriate to control the thickness of the bottom layer to 0.1-0.2mm and the thickness of the transition layer to 0.3-0.6mm. This is because if the thickness of the bottom layer is greater than 0.2mm, it is easy to cause warping deformation due to heat treatment, and if it is less than 0.1mm, it cannot support the transition layer. If the thickness of the transition layer is too small, the suspended part may also warp when forming the solid layer. If the thickness of the transition layer is too large, the forming efficiency will be reduced and the forming accuracy will be deteriorated.

[0017] Step 2: Slice the bottom layer of the suspended part, set the scanning mode to strip scanning, set the laser power to 200-230W, and set the scanning speed to 1200-1500mm / s. The reason why the parameter range is set in the above range is that it can ensure the forming accuracy of the bottom layer and reduce thermal stress deformation, providing a good base for the subsequent transition layer printing. If the laser power is less than the above range or the scanning speed exceeds the above range, the bottom layer will not be well formed and there will be a large number of pores. If a higher power or a lower speed is used, the thermal stress accumulation will be aggravated due to the high energy input, causing the bottom layer to have a large warping deformation.

[0018] Step three, slice the transition layer of the suspended part, set the scanning mode to chessboard scanning, and set layer-by-layer remelting. The transition layer scanning mode is set to chessboard scanning because strip scanning will form continuous stress accumulation on the forming surface, and multi-layer strip scanning will cause excessive stress accumulation and warping. Chessboard scanning can make the stress relatively discrete and uniformly distributed on the surface, eliminating the warping deformation caused by continuous stress accumulation. In addition, the laser power uses the same power as the subsequent physical layer, which can make the transition layer and the physical layer more firmly combined. Layer-by-layer remelting can smooth the rough surface formed by chessboard scanning, which is conducive to the forming of subsequent layers.

[0019] The inventors further discovered that by setting the laser power of the chessboard scan to 285W, the scanning speed to 1200-1500mm / s, and the chessboard vector number to 50-200, better stress-strain regulation effects can be achieved. When the scanning speed exceeds the above range, the powder bed cannot be fully melted, resulting in more pores. When the speed is too low, stress accumulation will increase and warping will occur. During the experiment, the inventors discovered that the chessboard vector number affects both stress accumulation and surface morphology. When the vector number is low, the surface flatness will be poor, affecting the forming accuracy. When the vector number is high, local thermal stress accumulation will be large and deformation will occur.

[0020] Step 4: Form the rest of the part using solid process parameters (laser power 285W, scanning speed 920-980mm / s). Example

[0021] The bottom of the suspended part of the model is divided into three layers, with a bottom layer thickness of 0.2 mm and a transition layer thickness of 0.6 mm. Each layer is sliced, and the slice thickness is 0.04 mm.

[0022] Using GH4169 alloy powder as raw material, the bottom layer process parameters are laser power 220W, scanning speed 1400mm / s, and scanning spacing 0.1mm.

[0023] The transition layer was scanned in a chessboard pattern with a vector number of 100. The process parameters were laser power 285W, scanning speed 1300mm / s, and scanning spacing 0.1mm. Strip scanning was used for layer-by-layer remelting. The remelting process parameters were laser power 285W, scanning speed 1300mm / s, and scanning spacing 0.1mm.

[0024] The process parameters for the rest of the parts and the physical layer are as follows: power 285W, scanning speed 960mm / s, scanning spacing 0.1mm, and scanning mode is strip scanning.

[0025] After forming, there is no warping or deformation in the suspended part, and the surface morphology is very smooth. Example

[0026] The bottom of the suspended part of the model is divided into three layers, with a bottom layer thickness of 0.2 mm, a transition layer thickness of 0.6 mm, and a slice thickness of 0.04 mm.

[0027] Using GH4169 alloy powder as raw material, the underlying process parameters are laser power 200W, scanning speed 1500mm / s, and scanning spacing 0.1mm.

[0028] The transition layer was scanned in a chessboard pattern with a vector number of 50. The process parameters were laser power 285W, scanning speed 1500mm / s, and scanning spacing 0.1mm. Strip scanning was used for layer-by-layer remelting. The remelting process parameters were laser power 285W, scanning speed 1500mm / s, and scanning spacing 0.1mm.

[0029] The process parameters of the physical layer are 285W, scanning speed 960mm / s, and scanning spacing 0.1mm.

[0030] After forming, there is no warping or deformation in the suspended part, and the surface morphology is relatively smooth.

[0031] Comparative Example 1 The bottom of the suspended part of the model is cut into two layers, the bottom layer is 0.2mm thick, and the rest are solid layers. No transition layer is set, and the slice thickness is 0.04mm.

[0032] Using GH4169 alloy powder as raw material, the underlying process parameters are laser power 200W, scanning speed 1500mm / s, and scanning spacing 0.1mm.

[0033] The physical layer process parameters are 285W, scanning speed 960mm / s, scanning spacing 0.1mm, and the scanning mode is strip scanning.

[0034] When the initial 2-3 layers of the solid layer are formed, the suspended part is obviously warped, which directly affects the scraper powder spreading process and causes the forming process to stop. This is because both the bottom layer and the solid layer are scanned in strips, which will form continuous stress accumulation on the forming surface. Multi-layer strip scanning will cause excessive stress accumulation and warping. As the number of forming layers increases, the stress accumulation gradually intensifies, eventually causing warping and deformation.

[0035] Comparative Example 2 Different from Example 1, the scanning speed of the bottom layer process parameters is 1600mm / s. When the solid layer is formed, the suspended part is obviously warped, which directly affects the scraper powder spreading process. The reason for the above result is that during the forming process, the bottom layer cannot form a relatively dense base at an excessively high scanning speed, so that when the transition layer is formed, the low-density bottom layer causes local collapse or deformation, affecting the forming accuracy.

[0036] Comparative Example 3 Different from Example 1, when scanning in a chessboard shape, the scanning speed is 1000 mm / s, the chessboard vector number is 45, and the surface accuracy of the suspended part after forming is poor and a certain deformation occurs. This is because, during the forming process of the transition layer, stress accumulation will be aggravated and warping deformation will occur. The low vector number causes irregular protrusions on the forming surface, and the surface protrusions cannot be eliminated by remelting, affecting the surface forming accuracy.

[0037] The above embodiments are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. The obvious changes or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A method for controlling stress and deformation of a hot end casing suspended structure prepared by selective laser melting, characterized in that: The steps include: Step 1: Divide the bottom of the suspended part of the hot end casing model into a bottom layer, a transition layer and a solid layer from bottom to top; Step 2: Slice the bottom layer of the suspended part, set the scanning mode to strip scanning, and use the printing device to print the bottom layer; Step 3: Slice the transition layer of the suspended part, set the scanning mode to chessboard scanning, and set layer-by-layer remelting. The remelting scanning mode adopts strip scanning, and use the printing equipment to print the transition layer; Step 4: The solid layer of the suspended part and the rest of the hot end casing model are formed using solid process parameters, and the scanning method is strip scanning to complete the preparation of the hot end casing.

2. The stress and deformation control method for preparing a hot end casing suspended structure by selective laser melting according to claim 1 is characterized in that: The thickness of the bottom layer is 0.1-0.2 mm, and the thickness of the transition layer is 0.3-0.6 mm.

3. The stress and deformation control method for preparing a hot end casing suspended structure by selective laser melting according to claim 2 is characterized in that: The thickness of the bottom layer is 0.2 mm, and the thickness of the transition layer is 0.5 mm.

4. The stress and deformation control method for preparing a hot end casing suspended structure by selective laser melting according to claim 1 is characterized in that: When printing the bottom layer of the suspended part, the laser power is set to 200-230W and the scanning speed is set to 1200-1500mm / s.

5. The stress and deformation control method for preparing a hot end casing suspended structure by selective laser melting according to claim 4 is characterized in that: When printing the bottom layer of the suspended part, the laser power is 220W and the scanning speed is 1400mm / s.

6. The stress and deformation control method for preparing a hot end casing suspended structure by selective laser melting according to claim 1 is characterized in that: The laser power of the chessboard scanning is set to 280-290W, the scanning speed is set to 1200-1500mm / s, the chessboard vector number is 50-200, and the laser power and scanning speed consistent with the chessboard scanning are used during layer-by-layer remelting.

7. The stress and deformation control method for preparing a hot end casing suspended structure by selective laser melting according to claim 6 is characterized in that: When scanning in a chessboard pattern, the laser power was set to 285 W, the number of chessboard vectors was 100, and the scanning speed was 1300 mm / s.

8. The stress and deformation control method for preparing a hot end casing suspended structure by selective laser melting according to claim 1 is characterized in that: The actual process parameters are laser power of 280-290W and scanning speed of 920-980mm / s.

9. The stress and deformation control method for preparing a hot end casing suspended structure by selective laser melting according to claim 8 is characterized in that: The actual process parameters are as follows: the laser power is 285W and the scanning speed is 960mm / s.

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