A method for improving the formability of 24CrNiMo alloy steel

Abstract

The invention discloses a method for improving the formability of 24CrNiMo alloy steel, relates to the technical field of additive manufacturing, and comprises the following steps: preparing alloy steel powder required for electron beam selective melting; constructing a three-dimensional part model; and printing the part under different preheating temperatures and process parameters. The method of the invention is based on preparing 24CrNiMo alloy steel by electron beam selective melting, and reduces the temperature gradient and thermal stress, effectively reduces the thermal stress of a formed specimen by changing the preheating temperature and regulating the process parameters of current beam, scanning speed, and powder bed sintering time, and refines the grains to achieve smooth and flat surface quality, high density, and few defects of the formed specimen.

Description

Technical Field

[0001] The invention relates to the technical field of additive manufacturing, and in particular to a method for improving the formability of 24CrNiMo alloy steel. Background Art

[0002] With the continuous development of high-speed trains, brake discs are key components for braking trains at high speeds, and they play a vital role. At present, the manufacturing methods used for brake discs of high-speed trains (>300km / h) in my country are forging and casting. However, due to the low yield of cast products and casting defects, the structural shape of forging methods is limited, and other problems, most brake discs currently rely mainly on imports.

[0003] Additive manufacturing technology is a rapid prototyping technology that uses a layer-by-layer accumulation method to manufacture solid parts. Based on its rapid prototyping, unrestricted structure of formed parts, and uniform formed structure, it has broad application prospects in aerospace, new energy materials, shipbuilding machinery and other fields. Electron beam selective melting technology is an additive manufacturing technology that uses electron beam as a heat source. Under the scanning of the electron beam, the metal powder is dissolved and solidified, and deposited layer by layer to manufacture three-dimensional metal parts. The substrate preheating step unique to the manufacturing process can effectively reduce the residual stress of the formed parts, reduce the temperature gradient, and refine the grains to prevent parts from cracking. If the energy density is too small, it will cause powder unmelted defects. If the energy density is too large, pores will appear due to the Marangoni effect. The appropriate energy density can reduce defects and the sample density is high. Summary of the invention

[0004] In order to overcome the shortcomings of the prior art, such as poor forming quality and many defects, the main purpose of the present invention is to provide a method for improving the formability of 24CrNiMo alloy steel.

[0005] To achieve the above object, the present invention adopts the following technical scheme, a method for improving the formability of 24CrNiMo alloy steel, the specific steps are as follows:

[0006] Constructing a model of a machined part made of alloy steel powder, slicing the model, saving the model in a plurality of triangular mesh formats, and importing the plurality of triangular mesh formats into an electron beam selective melting device;

[0007] According to several triangular mesh formats, the electron beam selective melting equipment prints and processes part models under different preheating temperatures and process parameters. The influencing factors of the process parameters include current beam, scanning speed and powder bed preheating and sintering time. The current beam is: 11.2-12.4mA, 12.8-13.5mA, 13-19mA; the scanning speed is: 5.2-6.4m / s, 6.2-6.6m / s, 5-6m / s; the minimum powder bed preheating and sintering time is 20-28s, the maximum powder bed preheating and sintering time is 25-35s, and the preheating temperature ranges from 820 to 920°C.

[0008] The electron beam selective melting equipment includes a powder bin and a forming bin, which are respectively filled with and substrate leveled, vacuumed, filled with protective gas, turned on high voltage and electron beam centered, substrate preheated, and process parameter set; wherein, the constructed model is printed after the substrate reaches the preheating temperature.

[0009] The invention also includes: preparing 24CrNiMo alloy steel powder required for electron beam selective melting; wherein the 24CrNiMo alloy steel powder is prepared by gas atomization, and the powder particle size range of the 24CrNiMo alloy steel is 50-120 μm, and the mass percentage of raw materials of the prepared 24CrNiMo alloy powder is: C: 0.2-0.25%, Cr: 0.9-1.25%, Ni: 0.9-1.3%, Si: 0.25-0.4%, Mo: 0.35-0.8%, Mn: 0.65-1.25%, and the balance is Fe element.

[0010] The selected preheating temperature is 820-920℃, and the factors affecting the process parameters include current flow, scanning speed and powder bed preheating sintering time. The powder bin and forming bin are filled and the substrate is leveled, vacuumed, protective gas is charged, high voltage is turned on, electron beam is centered, substrate is preheated, and process parameters are set. After the substrate reaches the preheating temperature, 24CrNiMo alloy steel is printed.

[0011] Preferably, the particle size of the powder of 24CrNiMo alloy steel prepared by gas atomization in step S1 is between 50 and 120 μm.

[0012] Preferably, the software for constructing the three-dimensional parts in step S2 is Materialise Magic, the sizes are 10×10×5mm, 12×12×8mm, 40×12×8mm, respectively, the slicing software is SL-EBM BuildPrepare, and the selected slice thickness is 50μm.

[0013] Preferably, the substrate preheating temperature selected in step S3 is 820-920°C, and the melting parameters selected for electron beam selective melting during the printing process are flow beam: 11.2-12.4mA, 12.8-13.5mA, 13-19mA; scanning speed: 5.2-6.4m / s, 6.2-6.6m / s, 5-6m / s. The minimum powder bed preheating sintering time used for powder bed preheating sintering during the printing process is 20-28s, and the maximum powder bed preheating sintering time is 25-35s. The purpose of powder bed preheating is to better consolidate the 24CrNiMo alloy steel on the surface of the powder bed, so that the forming quality is better and to prevent powder blowing and peeling during the printing process.

[0014] Preferably, the main operations in the substrate preheating process in step S3 are: the first stage: preheating the substrate to about 200°C with a current of 5mA and keeping it warm for 3 to 5 minutes; the second stage: adjusting the current to 10mA to preheat the substrate to about 500°C and keeping it warm for 5 to 8 minutes; the third stage: increasing the current to 15mA to preheat the substrate to about 700°C and keeping it warm for 10 minutes; the fourth stage: adjusting the current to 20 to 25mA to preheat the substrate to 820 to 920°C and keeping it warm for 10 to 15 minutes.

[0015] Preferably, the present invention mainly adjusts the preheating temperature, and the surface quality of the 24CrNiMo alloy steel printed at different preheating temperatures is different. Substrate preheating in additive manufacturing is an effective means to reduce thermal stress and the driving force of crack formation. As the preheating temperature increases, the temperature gradient and thermal stress decrease, it is beneficial to inhibit thermal cracks.

[0016] Preferably, the material selected for the substrate in step S3 is 316L stainless steel, and the vacuum degree of the electron beam forming chamber must reach 7.5×10 -1 The above, the protective gas is filled with helium for 2-3 minutes, the high voltage reaches 60kV, the scraper takes 0.09-0.10mm of powder each time, the electron beam spot diameter is 0.10mm, and the beam spot defocus is -0.500V.

[0017] Preferably, the present invention controls the process parameters by changing the current beam and the scanning speed to change the volume energy density of the electron beam selective melting. Increasing the power can reduce the temperature gradient of the molten pool, reduce the cooling rate, increase the cooling time, reduce the stress caused by shrinkage, and enhance the backfilling effect of the molten pool to inhibit the generation of cracks. The printed sample has the characteristics of high density, few defects, and good surface quality. The energy density can be changed by increasing the current beam (I) and reducing the scanning speed (v). The calculation formula of energy density is:

[0018]

[0019] Where U: voltage 60kV, I: current flow, v: scanning speed, d: scanning spacing 80mm, h: printing layer thickness 50μm. If the energy density is too low, it will cause powder unmelted defects, and if the energy density is too high, pore defects will appear due to the Marangoni effect. Appropriate energy density can reduce defects and the sample density is high.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] 1. The main method adopted by the present invention is the electron beam selective melting additive manufacturing technology with electron beam as the heat source. This method can provide high power and form in a vacuum environment to avoid oxidation due to excessive temperature. Under the appropriate process, the forming quality is high, the density is high, the grains are fine, and the structure is uniform.

[0022] 2. Since the forming quality, density, defects and cracks of electron beam selective melting are affected by the substrate preheating temperature and process parameters during the sample forming process, in order to solve the defects of unfused, pores, cracks and so on in the electron beam selective melting forming of 24CrNiMo alloy steel. The substrate preheating temperature is increased, the process parameters are adjusted to increase the energy density and the powder bed sintering time is controlled to achieve the quality of the formed parts, so as to achieve the smooth surface quality, high density and fine grains of the sample parts, so that its comprehensive performance is improved.

[0023] 3. The present invention manufactures 24CrNiMo alloy steel by electron beam selective melting, and by adjusting the preheating temperature and process parameters, compared with the traditional method, it can effectively overcome the Casting Defects formed during the process, low yield, and limitations caused by the complex structure of the formed parts during the forging process. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a formed sample of the present invention at a substrate temperature of 820°C;

[0025] Figure 2 It is a formed sample of the present invention at a substrate temperature of 900°C;

[0026] Figure 3 It is a formed sample of the present invention at a substrate temperature of 870°C;

[0027] Figure 4 It is a schematic diagram of the process and structure of the present invention. DETAILED DESCRIPTION

[0028] The present invention will be further described below in conjunction with the accompanying drawings and implementation modes.

[0029] Example:

[0030] See also Figure 1-4, a method for improving the formability of 24CrNiMo alloy steel, comprising the following steps:

[0031] S1. Prepare alloy steel powder required for electron beam selective melting; wherein the required 24CrNiMo alloy powder is prepared by gas atomization, and the raw material mass percentages of the prepared 24CrNiMo alloy powder are: C: 0.2-0.25%, Cr: 0.9-1.25%, Ni: 0.9-1.3%, Si: 0.25-0.4%, Mo: 0.35-0.8%, Mn: 0.65-1.25%, and the balance is Fe element;

[0032] S2, build a 3D part model, build a 3D processing platform, and process the parts in sequence. Slice and plan the constructed parts to form an SLT format, and import them into the electron beam selective melting equipment;

[0033] S3, printing parts under different preheating temperatures and process parameters;

[0034] The selected preheating temperature is 820℃, and the factors affecting the process parameters include current flow, scanning speed and powder bed preheating sintering time. The powder bin and forming bin are filled and the substrate is leveled, vacuumed, protective gas is charged, high voltage is turned on, electron beam is centered, the substrate is preheated, and process parameters are set. After the substrate reaches the preheating temperature, 24CrNiMo alloy steel is printed.

[0035] The particle size of the powder of 24CrNiMo alloy steel prepared by gas atomization in step S1 is between 50 and 120 μm.

[0036] The software used to construct the three-dimensional part in step S2 is Materialise Magic, the size is 10×10×5 mm, the slicing software is SL-EBM BuildPrepare, and the selected slice thickness is 50 μm.

[0037] The substrate preheating temperature selected in step S3 is 820°C, and the melting parameters selected by the electron beam selective melting during the printing process are flow beam: 11.2~12.4mA scanning speed: 5.2~6.4m / s. The minimum powder bed preheating sintering time used for powder bed preheating sintering during the printing process is 20s, and the maximum powder bed preheating sintering time is 25s. The purpose of powder bed preheating is to better consolidate the 24CrNiMo alloy steel on the surface of the powder bed, so that the forming quality is better and to prevent powder blowing and peeling during the printing process.

[0038] The main operations in the substrate preheating process in step S3 are: the first stage: preheating the substrate to about 200°C with a current of 5mA and keeping it warm for 3 minutes; the second stage: adjusting the current to 10mA to preheat the substrate to about 500°C and keeping it warm for 5 minutes; the third stage: increasing the current to 15mA to preheat the substrate to about 700°C and keeping it warm for 10 minutes; the fourth stage: adjusting the current to 20mA to preheat the substrate to 820°C and keeping it warm for 10 minutes.

[0039] The present invention mainly adjusts the preheating temperature. The surface quality of the 24CrNiMo alloy steel printed at different preheating temperatures is different. Substrate preheating in additive manufacturing is an effective means to reduce thermal stress and the driving force of crack formation. With the increase of preheating temperature, the temperature gradient and thermal stress are reduced, which is conducive to inhibiting thermal cracks.

[0040] In step S3, the material selected for the substrate is 316L stainless steel, the vacuum degree of the electron beam forming chamber must reach 7.5×10-1 or above, the protective gas is helium for 2 minutes, and the high voltage reaches 60kV. The scraper takes 0.09mm of powder each time, the electron beam spot diameter is 0.10mm, and the beam spot defocus is -0.500V.

[0041] The present invention controls the process parameters by changing the current beam and the scanning speed to change the volume energy density of the electron beam selective melting. Increasing the power can reduce the temperature gradient of the molten pool, reduce the cooling rate, increase the cooling time, reduce the stress caused by shrinkage, and enhance the backfilling effect of the molten pool to inhibit the generation of cracks. The printed sample has the characteristics of high density, few defects and good surface quality. The energy density can be changed by increasing the current beam (I) and reducing the scanning speed (v). The calculation formula of energy density is:

[0042]

[0043] Wherein U: voltage 60kV, I: current flow, v: scanning speed, d: scanning spacing 80mm, h: printing layer thickness 50μm.

[0044] In this example, at the preheating temperature of 820℃, the minimum energy density is 26.3J / mm3 and the maximum energy density is 35.8J / mm3. If the energy density is too low, the powder will not be melted, and if the energy density is too high, the defect of pores will appear due to the Marangoni effect. The appropriate energy density can reduce the defects and the sample has a high density.

[0045] Embodiment 2:

[0046] A method for improving the formability of 24CrNiMo alloy steel comprises the following steps:

[0047] S1. Preparation of alloy steel powder required for electron beam selective melting

[0048] The 24CrNiMo alloy powder used in the present invention is prepared by gas atomization. The raw materials of the prepared 24CrNiMo alloy powder are as follows: C: 0.2-0.25%, Cr: 0.9-1.25%, Ni: 0.9-1.3%, Si: 0.25-0.4%, Mo: 0.35-0.8%, Mn: 0.65-1.25%, and the balance is Fe element;

[0049] S2. Build 3D part model

[0050] Build the 3D processing platform and process the parts in sequence. Slice and plan the constructed parts to form SLT format, and import them into the electron beam selective melting equipment;

[0051] S3, printing parts under different preheating temperatures and process parameters;

[0052] The selected preheating temperature is 870℃, and the factors affecting the process parameters include current flow, scanning speed and powder bed preheating sintering time. The powder bin and forming bin are filled and the substrate is leveled, vacuumed, protective gas is charged, high voltage is turned on, electron beam is centered, the substrate is preheated, and process parameters are set. After the substrate reaches the preheating temperature, 24CrNiMo alloy steel is printed.

[0053] The particle size of the powder of 24CrNiMo alloy steel prepared by gas atomization in step S1 is between 50 and 120 μm.

[0054] The software used to construct the three-dimensional part in step S2 is Materialise Magic, with a size of 12×12×8 mm. The slicing software is SL-EBM BuildPrepare, and the selected slice thickness is 50 μm.

[0055] The substrate preheating temperature selected in step S3 is 870°C, and the melting parameters selected for electron beam selective melting during the printing process are flow beam: 12.8-13.5 mA scanning speed: 6.2-6.4 m / s. The minimum powder bed preheating sintering time used for powder bed preheating sintering during the printing process is 24s, and the maximum powder bed preheating sintering time is 30s. The purpose of powder bed preheating is to better consolidate the 24CrNiMo alloy steel on the surface of the powder bed, so that the forming quality is better and to prevent powder blowing and peeling during the printing process.

[0056] The main operations in the substrate preheating process in step S3 are: the first stage: preheating the substrate to about 200°C with a current of 5mA and keeping it warm for 4 minutes; the second stage: adjusting the current to 10mA to preheat the substrate to about 500°C and keeping it warm for 8 minutes; the third stage: increasing the current to 15mA to preheat the substrate to about 700°C and keeping it warm for 10 minutes; the fourth stage: adjusting the current to 20mA to preheat the substrate to 820°C and keeping it warm for 15 minutes.

[0057] The present invention mainly adjusts the preheating temperature. The surface quality of the 24CrNiMo alloy steel printed at different preheating temperatures is different. Substrate preheating in additive manufacturing is an effective means to reduce thermal stress and the driving force of crack formation. With the increase of preheating temperature, the temperature gradient and thermal stress are reduced, which is conducive to inhibiting thermal cracks.

[0058] Preferably, the material selected for the substrate in step S3 is 316L stainless steel, the vacuum degree of the electron beam forming chamber must reach 7.5×10-1 or more, the protective gas is helium for 3 minutes, and the high voltage reaches 60kV. The scraper takes 0.095mm of powder each time, the electron beam spot diameter is 0.10mm, and the beam spot defocus is -0.500V.

[0059] Preferably, the present invention controls the process parameters by changing the current beam and the scanning speed to change the volume energy density of the electron beam selective melting. Increasing the power can reduce the temperature gradient of the molten pool, reduce the cooling rate, increase the cooling time, reduce the stress caused by shrinkage, and enhance the backfilling effect of the molten pool to inhibit the generation of cracks. The printed sample has the characteristics of high density, few defects, and good surface quality. The energy density can be changed by increasing the current beam (I) and reducing the scanning speed (v). The calculation formula of energy density is:

[0060]

[0061] Among them, U is voltage 60kV, I is current flow, v is scanning speed, d is scanning spacing 80mm, and h is printing layer thickness 50μm.

[0062] In this example, at a preheating temperature of 870°C, the minimum energy density is 29.1 J / mm3 and the maximum energy density is 32.6 J / mm3. If the energy density is too low, the powder will not be melted, and if the energy density is too high, the defect of pores will appear due to the Marangoni effect. The appropriate energy density can reduce the defects and the sample has a high density.

[0063] Embodiment 3:

[0064] A method for improving the formability of 24CrNiMo alloy steel comprises the following steps:

[0065] S1. Preparation of alloy steel powder required for electron beam selective melting

[0066] The 24CrNiMo alloy powder used in the present invention is prepared by gas atomization. The raw materials of the prepared 24CrNiMo alloy powder are as follows: C: 0.2-0.25%, Cr: 0.9-1.25%, Ni: 0.9-1.3%, Si: 0.25-0.4%, Mo: 0.35-0.8%, Mn: 0.65-1.25%, and the balance is Fe element;

[0067] S2. Build 3D part model

[0068] Build the 3D processing platform and process the parts in sequence. Slice and plan the constructed parts to form SLT format, and import them into the electron beam selective melting equipment;

[0069] S3, printing parts under different preheating temperatures and process parameters;

[0070] The selected preheating temperature is 920℃, and the factors affecting the process parameters include current flow, scanning speed and powder bed preheating sintering time. The powder bin and forming bin are filled and the substrate is leveled, vacuumed, protective gas is charged, high voltage is turned on, electron beam is centered, the substrate is preheated, and process parameters are set. After the substrate reaches the preheating temperature, 24CrNiMo alloy steel is printed.

[0071] The particle size of the powder of 24CrNiMo alloy steel prepared by gas atomization in step S1 is between 50 and 120 μm.

[0072] Preferably, the software for constructing the three-dimensional part in step S2 is Materialise Magic, the size is 40×15×8 mm, the slicing software is SL-EBM BuildPrepare, and the selected slice thickness is 50 μm.

[0073] The substrate preheating temperature selected in step S3 is 820°C, and the melting parameters selected by the electron beam selective melting during the printing process are flow beam: 13-19mA scanning speed: 5-6m / s. The minimum powder bed preheating sintering time used for the powder bed preheating sintering during the printing process is 28s, and the maximum powder bed preheating sintering time is 35s. The purpose of powder bed preheating is to better consolidate the 24CrNiMo alloy steel on the surface of the powder bed, so that the forming quality is better and to prevent the powder blowing and peeling phenomenon during the printing process.

[0074] Preferably, the main operations in the substrate preheating process in step S3 are: the first stage: preheating the substrate to about 200°C with a current of 5mA and keeping it warm for 5 minutes; the second stage: adjusting the current to 10mA to preheat the substrate to about 500°C and keeping it warm for 8 minutes; the third stage: increasing the current to 15mA to preheat the substrate to about 700°C and keeping it warm for 15 minutes; the fourth stage: adjusting the current to 25mA to preheat the substrate to 920°C and keeping it warm for 15 minutes.

[0075] The present invention mainly adjusts the preheating temperature. The surface quality of the 24CrNiMo alloy steel printed at different preheating temperatures is different. Substrate preheating in additive manufacturing is an effective means to reduce thermal stress and the driving force of crack formation. With the increase of preheating temperature, the temperature gradient and thermal stress are reduced, which is conducive to inhibiting thermal cracks.

[0076] In step S3, the material selected for the substrate is 316L stainless steel, the vacuum degree of the electron beam forming chamber must reach 7.5×10-1 or above, the protective gas is helium for 5 minutes, and the high voltage reaches 60kV. The scraper takes 0.10mm of powder each time, the electron beam spot diameter is 0.10mm, and the beam spot defocus is -0.500V.

[0077] The present invention controls the process parameters by changing the current beam and the scanning speed to change the volume energy density of the electron beam selective melting. Increasing the power can reduce the temperature gradient of the molten pool, reduce the cooling rate, increase the cooling time, reduce the stress caused by shrinkage, and enhance the backfilling effect of the molten pool to inhibit the generation of cracks. The printed sample has the characteristics of high density, few defects and good surface quality. The energy density can be changed by increasing the current beam (I) and reducing the scanning speed (v). The calculation formula of energy density is:

[0078] Wherein U: voltage 60kV, I: current flow, v: scanning speed, d: scanning spacing 80mm, h: printing layer thickness 50μm.

[0079] In this example, at a preheating temperature of 920°C, the minimum energy density is 32.5 J / mm3 and the maximum energy density is 57 J / mm3. If the energy density is too low, the powder will not be melted, and if the energy density is too high, the defect of pores will appear due to the Marangoni effect. The appropriate energy density can reduce the defects and the sample has a high density.

[0080] It should be noted that, in the present invention, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0081] The above embodiments are merely examples of the present invention and do not limit the protection scope of the present invention. All designs that are the same or similar to the present invention fall within the protection scope of the present invention.

Claims

1. A method for improving the formability of 24CrNiMo alloy steel, characterized in that: The following steps are involved: Constructing a model of a part to be processed by alloy steel powder, slicing the model, saving the model in a plurality of triangular mesh formats, and importing the plurality of triangular mesh formats into an electron beam selective melting device; According to a number of triangular mesh formats, the electron beam selective melting device prints and processes part models at different preheating temperatures and process parameters; The process parameters influencing factors include current beam, scanning speed and powder bed preheating and sintering time. The current flow is 11.2-12.4 mA, and the scanning speed is 5.2-6.4 m / s; or the current flow is 12.8-13.5 mA, and the scanning speed is 6.2-6.4 m / s; or the current flow is 13-19 mA, and the scanning speed is 5-6 m / s; the minimum powder bed preheating and sintering time is 20-24 s, and the maximum powder bed preheating and sintering time is 25-35 s; The invention also includes: preparing 24CrNiMo alloy steel powder required for electron beam selective melting; wherein the raw materials of the prepared 24CrNiMo alloy steel powder are as follows: C: 0.2-0.25%, Cr: 0.9-1.25%, Ni: 0.9-1.3%, Si: 0.25-0.4%, Mo: 0.35-0.8%, Mn: 0.65-1.25%, and the balance is Fe element; The 24CrNiMo alloy steel powder is prepared by gas atomization, and the powder particle size of the 24CrNiMo alloy steel is in the range of 50 to 120 μm; After the substrate reaches the preheating temperature, the built model begins to be printed; Substrate preheating includes the following steps: Preheat the substrate to 200°C with 5 mA current and keep it warm for 3-5 minutes; Adjust the current to 10mA to preheat the substrate to 500℃ and keep it warm for 5~8min; The current was increased to 15 mA to preheat the substrate to 700°C and keep it for 10 min; Adjust the current to 20~25mA to preheat the substrate to 820~920℃ and keep it warm for 10~15min; The vacuum degree of the electron beam forming chamber in the electron beam selective melting equipment reaches 7.5×10 -1 In the above, helium is selected as the protective gas, and the filling time ranges from 2 to 3 minutes; the electron beam spot diameter is 0.10mm, and the beam spot defocus is: -0.500V.

2. A method for improving the formability of 24CrNiMo alloy steel according to claim 1, characterized in that: The improvement of the energy density of electron beam selective melting in the electron beam selective melting device is achieved by increasing the current beam and reducing the scanning speed; the calculation formula of the energy density is as follows: ； Among them, U is the voltage of 60kV, I is the current flow, v is the scanning speed, d is the scanning spacing of 80mm, and h is the printing layer thickness of 50μm.

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