Additive manufacturing methods for metallic materials

Abstract

This invention provides an additive manufacturing method for metallic materials. By dividing the printing of parts into units and dynamically adjusting the printing unit energy of each unit, the printing unit energy is controlled within the critical unit energy range. By controlling the energy density input per unit time during printing within a suitable range, overheating is avoided, and warping deformation caused by excessive internal residual stress is prevented. The resulting parts have good forming quality and ensure the mechanical properties of the formed parts, while improving printing efficiency and reducing costs.

Description

Technical Field

[0001] This invention relates to the field of additive manufacturing technology, and more specifically to an additive manufacturing method for metallic materials. Background Technology

[0002] Laser powder bed melting (LPBF) is an advanced metal additive manufacturing technology that uses a high-energy laser beam to melt metal powder layer by layer, building complex metal parts through a stacking process. LPBF technology not only boasts high precision and high quality but also enables the direct fabrication of parts with optimized internal structures and complex geometries, greatly meeting the demands of aerospace, automotive, and other fields for high-performance metal components. Furthermore, LPBF technology offers advantages such as high material utilization and short production cycles, bringing revolutionary changes to modern manufacturing.

[0003] In the LPBF process, for certain thin plate structures with an angle to the horizontal plane, in the traditional laser selective melting process, when the angle is less than 40 degrees (low angle), supports are often needed to ensure heat dissipation and prevent the parts from collapsing. However, adding supports increases manufacturing time, material waste, and post-processing difficulty. If the added supports are reduced, the parts will overheat and warp. This is because after each layer is printed, some areas are in contact with metal powder. The thermal conductivity of metal powder is lower than that of the metal solid. Therefore, during the printing process, energy accumulates in the areas in contact with the metal powder, and the accumulated heat leads to overheating, ultimately causing the parts to overheat, warp, and deform, resulting in forming failure.

[0004] To address the issue of reducing component deformation in low-angle printed parts due to support deformation, researchers have attempted to improve the situation through topology optimization. For example, Dong Yongjia et al. proposed a novel topology optimization method that considers support constraints in additive manufacturing within a density-based topology optimization framework and reduces the volume of the support structure through mathematical models and algorithms. Wu Shuting et al. proposed constraints and design rules for lightweight part design based on SLM technology. Taking a satellite heat sink as an example, they conducted finite element analysis and topology optimization design, reducing weight and improving performance through structural optimization. While structural optimization solves some problems, the structure of some parts is already optimal or cannot be optimized due to certain circumstances.

[0005] In addition, researchers have also attempted to address the overheating problem during small-angle printing through process optimization. For example, the supportless laser selective melting additive manufacturing method disclosed in Chinese patent CN117182106A involves pre-sintering the first layer, then sintering the solid, repeating this process 1-20 times before printing the solid. Although this method can reduce the need for supports, it may result in porosity during the first sintering process. These porosity may not be eliminated during the second sintering process, resulting in defects. Furthermore, it requires repeated scanning, leading to excessively long printing times and low efficiency.

[0006] For example, the SLM unsupported forming method for high-temperature alloy cross-section abrupt structure disclosed in Chinese patent CN114406286A uses a small energy density to achieve unsupported planar overhanging structure of high-temperature alloy. However, although the process optimization method of reducing a certain part of the energy avoids the occurrence of overheating, the reduction of energy leads to increased porosity and decreased mechanical properties.

[0007] In the additive manufacturing process of metal materials, how to avoid the warping and deformation of parts remains a difficult problem to solve. Although existing technologies attempt to solve the problems of stress concentration and warping and deformation caused by overheating through topology optimization and energy density optimization, they are still not ideal. Summary of the Invention

[0008] The purpose of this invention is to address the shortcomings of existing technologies by providing an additive manufacturing method for metal materials. This method involves modularizing the printing of parts and dynamically adjusting the printing energy per unit volume. By adjusting the energy within a unit volume, the energy density input per unit time is kept within a suitable range, avoiding overheating and warping caused by excessive internal residual stress. This results in high-quality parts with guaranteed mechanical properties, while also improving printing efficiency and reducing costs.

[0009] According to a first aspect of the present invention, an additive manufacturing method for a metallic material is provided, comprising the following steps:

[0010] The scan line distance and printing layer thickness were determined, and then metal block samples were printed with different laser powers and scanning speeds. The critical laser power P was determined based on the microstructure analysis of the metal block samples. max and critical scan rate v max And determine the minimum acceptable laser power P Amin and maximum acceptable scan speed v Amax Among them, P max >P Amin v max <v Amax ;

[0011] Under the same scan line distance and printing layer thickness, with P max and v max E represents the energy required to obtain the volume formed per unit time when printing with the same metal material, as a combination of laser power and scanning speed. max ;

[0012] The part to be formed is decomposed into several printing units. Each printing unit is analyzed to determine the laser power and scanning speed corresponding to each printing unit, and the corresponding unit is printed until the part is formed.

[0013] The process of analyzing the printing unit includes:

[0014] Under the same scan line distance and printed layer thickness, with empirical laser power P exp and experience scan speed v exp As laser power and scanning speed, the energy of the forming volume per unit time of the printing unit is determined when printing with the same metal raw material, denoted as E. exp ;

[0015] For any printable cell:

[0016] If E in the printing unit exp ≤E max Then use P exp and v exp The current cell is printed using laser power and scanning speed;

[0017] If E in the printing unit exp >E max Then, by reducing the laser power and / or increasing the scanning speed, E exp ≤E max ;in,

[0018] When P Amin ≤ Adjusted final laser power < P exp , and v Amax ≤ Adjusted final scan speed < v exp If the laser power and scanning speed are adjusted, the current unit will be printed.

[0019] When the final adjusted laser power < P Amin And the adjusted final scan speed > v Amax When, then P is used. Amin and v Amax The current cell is printed using the final laser power and final scanning speed, and the laser forced delay is turned off during the printing process, so that the E in the cell... exp ≤E max .

[0020] As an optional implementation method, the energy of the formed volume per unit time is calculated according to formula (1):

[0021]

[0022] In the formula, E represents the energy of the formed volume per unit time, in J / mm². 3 •s; P is laser power, W; v is scanning speed, mm / s; D is scan line distance, mm; L is printing layer thickness, mm; T is printing time, s; V is printing volume, mm. 3 .

[0023] As an optional implementation, the printing time T is calculated according to formula (2):

[0024]

[0025] In the formula, T is the printing time (s); l is the total length of the printed layer (mm); v is the scanning speed (mm / s); t is the pause time between adjacent printed layers (s); and N is the number of printed layers.

[0026] As an optional implementation, the laser forced delay is turned off during the printing process, and the extended time is determined by the following method:

[0027] Using P Amin and v Amax E is obtained from the laser power and scanning time using formula (1). max The printing time T1 is obtained by formula (2), and the extended time is T1-T2.

[0028] As an optional implementation, in the guarantee unit E exp ≤E max Under the premise of this, determine the printing extension time of the current cell and allocate it to the printing layer of the current cell for the delay.

[0029] As an optional implementation, the delay is allocated to the printing layer, including:

[0030] The delay time is evenly distributed to each printing layer of the current unit, with a delay between 25% and 75% of the printing area of ​​each printing layer completed, and the dwell positions of different printing layers do not overlap.

[0031] As an optional implementation, the critical laser power P is determined. max and critical scan rate v max include:

[0032] The scanning line distance and printing layer thickness were determined, and metal block samples were printed using different laser powers and scanning speeds. The metallographic structure of each sample was analyzed. The presence or absence of Widmanstätten structure was used as the dividing line, and the laser power and scanning speed corresponding to the sample without Widmanstätten structure were taken as the critical laser power P. max and critical scan rate v max .

[0033] As an optional implementation, the minimum acceptable laser power P is determined. Amin and maximum acceptable scan speed v Amax include:

[0034] The scanning line distance and printing layer thickness were determined, and metal block samples were printed using different laser powers and scanning speeds. The metallographic structure of each sample was analyzed. The boundary between samples with a porosity of less than or equal to 5‰ and those with a porosity greater than 5‰ was used. The laser power and scanning speed corresponding to the samples with a porosity of less than or equal to 5‰ were taken as the minimum acceptable laser power P. Amin and maximum acceptable scan speed v Amax .

[0035] According to a second aspect of the present invention, a method for manufacturing a metal part having a drooping structure is provided, comprising an additive manufacturing method for the metal material as described in any one of claims 1-8.

[0036] As an optional implementation, during preparation, columnar support members with a diameter of 0.3 to 0.5 mm are provided along the edge of the suspended structure, and the interval between adjacent support members is 5 to 10 mm.

[0037] As can be seen from the above technical solution of the present invention, the additive manufacturing method for metal materials proposed in this invention unitizes the printing of parts and dynamically adjusts the printing unit energy of each unit to control the printing unit energy within the critical unit energy. By controlling the energy density input per unit time during printing within a suitable range, overheating is avoided, and warping deformation caused by excessive internal residual stress is prevented. The part forming quality is good, and the mechanical properties of the formed part are guaranteed. At the same time, printing efficiency is improved, subsequent processing is simplified, and costs are reduced. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of a suspended structure that forms an angle with the horizontal plane, as shown in an example of the present invention.

[0039] Figure 2 This is a process flow diagram of the additive manufacturing method for metallic materials according to the present invention.

[0040] Figure 3 and Figure 4These are, respectively, dimensional structural diagrams of the printed parts in embodiments of the present invention; wherein, Figure 3 It is a front view. Figure 4 It is a top view.

[0041] Figure 5 This refers to determining the critical laser power P in Embodiment 1 of the present invention. max and critical scan rate v max Metallographic diagram of the corresponding sample.

[0042] Figure 6 The minimum acceptable laser power P is determined in Embodiment 1 of the present invention. Amin and maximum acceptable scan speed v Amax Metallographic diagram of the corresponding sample.

[0043] Figure 7 and Figure 8 These are schematic diagrams of the support structure in Embodiment 1 of the present invention; wherein, Figure 8 It is a front view. Figure 9 It is a top view.

[0044] Figure 9 and Figure 10 These are schematic diagrams of the support structure in Comparative Example 1 of the present invention; wherein, Figure 9 It is a front view. Figure 10 It is a top view.

[0045] Figure 11 This is a printed physical image of the part used in Comparative Example 2 of this invention.

[0046] Figure 12 This is a printed physical image of the part according to Embodiment 1 of the present invention. Detailed Implementation

[0047] To better understand the technical content of the present invention, specific embodiments are described below in conjunction with the accompanying drawings.

[0048] Various aspects of the invention are described in this disclosure with reference to the accompanying drawings, in which numerous illustrative embodiments are shown. The embodiments of this disclosure are not necessarily intended to encompass all aspects of the invention. It should be understood that the various concepts and embodiments described above, as well as those described below in more detail, can be implemented in any of a number of ways.

[0049] Combination Figure 1As shown, taking the printing of a suspended structure with an angle (α) to the horizontal plane using laser powder bed melting technology as an example, powder is laid on substrate 1 for printing. Due to the existence of the suspended structure, some powder on certain printing layers does not need to be melted and deposited, and remains in its original state. When printing the next printing layer, the powder at the next layer position needs to be melted and deposited, so the printed part will form a solid part and a powder part 2. The suspended structure will have three situations: the area without a part in the upper layer in the Z direction is called the upper surface 3; the area without a part in the lower layer in the Z direction is called the lower surface 4; and all other than the upper and lower surfaces are called the inner surface 5.

[0050] The solid area in contact with the inner surface of the current layer dissipates heat faster than the powder area in contact with the lower surface of the current layer. Therefore, if the printing heat is too high, excessive heat will accumulate on the lower surface area, eventually leading to defects such as warping and deformation of the parts.

[0051] Therefore, this invention constructs a dynamic energy adjustment strategy that reduces the energy input in high-energy regions during part printing without changing the energy region of low-stress regions. This strategy determines the energy density input per unit time, and if it is too high, it adjusts the energy input in high-energy regions without changing the energy region of low-stress regions. This can achieve no increase or even reduction in printing time, while not requiring excessive energy reduction to ensure the mechanical properties of the parts.

[0052] It is understood that the method of the present invention is applicable to additive manufacturing of metal materials heated by high-energy heat sources, such as using lasers, electron beams, plasma arcs, etc. as heat sources to heat and melt metal powders or metal wires.

[0053] like Figure 2 As shown, in a preferred embodiment of the present invention, an additive manufacturing method for a metallic material is provided, comprising the following steps:

[0054] The scan line distance and printing layer thickness were determined, and then metal block samples were printed with different laser powers and scanning speeds. The critical laser power P was determined based on the microstructure analysis of the metal block samples. max and critical scan rate v max And determine the minimum acceptable laser power P Amin and maximum acceptable scan speed v Amax Among them, P max >P Amin v max <v Amax .

[0055] As an optional example, determining the critical laser power P max and critical scan rate v maxinclude:

[0056] The scanning line distance and printing layer thickness were determined, and metal block samples were printed using different laser powers and scanning speeds. The metallographic structure of each sample was analyzed. The presence or absence of Widmanstätten structure was used as the dividing line, and the laser power and scanning speed corresponding to the sample without Widmanstätten structure were taken as the critical laser power P. max and critical scan rate v max .

[0057] As an optional example, determine the minimum acceptable laser power P. Amin and maximum acceptable scan speed v Amax include:

[0058] The scanning line distance and printing layer thickness were determined, and metal block samples were printed using different laser powers and scanning speeds. The metallographic structure of each sample was analyzed. The boundary between samples with a porosity of less than or equal to 5‰ and those with a porosity greater than 5‰ was used. The laser power and scanning speed corresponding to the samples with a porosity of less than or equal to 5‰ were taken as the minimum acceptable laser power P. Amin and maximum acceptable scan speed v Amax .

[0059] As a preferred example, the critical laser power P can be determined using an orthogonal experiment. max and critical scan rate v max and minimum acceptable laser power P Amin and maximum acceptable scan speed v Amax The determination of these parameters is understandable. One approach is to set up a single orthogonal experiment to obtain all four parameters simultaneously, or two orthogonal experiments can be set up to obtain the critical laser power P separately. max and critical scan rate v max and minimum acceptable laser power P Amin and maximum acceptable scan speed v Amax .

[0060] Subsequently, under the same scan line distance and printing layer thickness conditions, with P max and v max E represents the energy required to obtain the volume formed per unit time when printing with the same metal material, as a combination of laser power and scanning speed. max .

[0061] After determining E max P Amin and v Amax Next, the part to be formed is decomposed into several printing units. Each printing unit is analyzed to determine the laser power and scanning speed corresponding to each printing unit, and the corresponding unit is printed until the part is formed.

[0062] The process of analyzing the printing unit includes:

[0063] Under the same scan line distance and printed layer thickness, with empirical laser power P exp and experience scan speed v exp As laser power and scanning speed, the energy of the forming volume per unit time of the printing unit is determined when printing with the same metal raw material, denoted as E. exp ;

[0064] For any printable cell:

[0065] If E in the printing unit exp ≤E max Then use P exp and v exp The current cell is printed using laser power and scanning speed;

[0066] If E in the printing unit exp >E max Then, by reducing the laser power and / or increasing the scanning speed, E exp ≤E max ;in,

[0067] When P Amin ≤ Adjusted final laser power < P exp , and v Amax ≤ Adjusted final scan speed < v exp If the laser power and scanning speed are adjusted, the current unit will be printed.

[0068] When the final adjusted laser power < P Amin And the adjusted final scan speed > v Amax When, then P is used. Amin and v Amax The current cell is printed using the final laser power and final scanning speed, and the laser forced delay is turned off during the printing process, so that the E in the cell... exp ≤E max .

[0069] In the aforementioned process, the scan line distance, the printing layer, and the empirical laser power P exp and experience scan speed v exp The determination process is as follows:

[0070] First, determine the printing layer thickness. The common printing layer thickness range is generally between 0.1mm and 0.5mm. For example, for prints that require high precision and detail, you can choose a layer thickness of 0.1mm or thinner; while for prints with high time requirements, you can choose a layer thickness of 0.3mm or thicker.

[0071] After determining the printing layer thickness, the laser power required to completely melt the metal material at that thickness is determined based on the layer thickness and the type of raw material. Generally, metals with higher melting points have higher energy densities than those with lower melting points. For example, at a layer thickness of 0.06mm, stainless steel may require 400W to completely melt, while titanium / aluminum alloys generally require 200W or more. Although copper alloys have a low melting point, their poor light absorption necessitates a relatively high power of 400W for melting. Single-channel tests can be performed at different laser powers, and multi-channel tests can be conducted using the laser power required to completely fuse a single channel. The required scan line distance is determined by using the scan line distance that allows adjacent channels to form a plane.

[0072] Subsequently, at the determined scan line distance and printing layer thickness, block-shaped samples were printed. The laser power and scanning speed corresponding to samples with low surface roughness were used as empirical laser power P. exp and experience scan speed v exp .

[0073] Understandable, scan line distance, printing layers, and empirical laser power P exp and experience scan speed v exp The parameters can be determined using the methods described above, or commonly used production parameters can be directly adopted. Each company has its own commonly used production parameters, and empirical values ​​or parameters recorded in the literature can be used directly.

[0074] As an optional example, the energy of the formed volume per unit time is calculated according to formula (1):

[0075]

[0076] In the formula, E represents the volume formed per unit time, in J / mm². 3 •s; P is laser power, W; v is scanning speed, mm / s; D is scan line distance, mm; L is printing layer thickness, mm; T is printing time, s; V is printing volume, mm. 3 .

[0077] As an optional example, the printing time T is calculated according to formula (2):

[0078]

[0079] In the formula, T is the printing time (s); l is the total length of the printed layer (mm); v is the scanning speed (mm / s); t is the pause time between adjacent printed layers (s); and N is the number of printed layers.

[0080] As an optional example, the laser forced delay is turned off during the printing process, and the extended time is determined by the following method:

[0081] Using PAmin and v Amax E is obtained from the laser power and scanning time using formula (1). max The printing time T1 is obtained by formula (2), and the extended time is T1-T2.

[0082] As an optional example, in the guaranteed unit E exp ≤E max Under the premise of this, determine the printing extension time of the current cell and allocate it to the printing layer of the current cell for the delay.

[0083] As an optional example, the delay assigned to the print layer includes:

[0084] The delay time is evenly distributed to each printing layer of the current unit, with a delay between 25% and 75% of the printing area of ​​each printing layer completed, and the dwell positions of different printing layers do not overlap.

[0085] In another preferred embodiment, a method for preparing a metal part with a drooping structure is also provided, including the aforementioned additive manufacturing method for the metal material.

[0086] As an optional example, during fabrication, columnar supports with a diameter of 0.3 to 0.5 mm are provided along the edge of the overhanging structure, with a spacing of 5 to 10 mm between adjacent supports.

[0087] In one typical example, using the aforementioned additive manufacturing method for metallic materials, a part with a hanging structure is printed using laser powder bed melting technology. The manufacturing process includes the following specific steps:

[0088] (1) Determine the critical value: Before printing the part, it is necessary to determine the maximum critical energy input per unit volume per second. The method for determination is as follows:

[0089] Determine the required scan line distance D1 and printing layer thickness L1 for the printed part. Design orthogonal experiments with different laser powers and scanning speeds. Print the corresponding metal sample using powder-spreading. The sample is a cube with a side length of 10 mm. Record the printing process time.

[0090] After the cube was cut from the substrate, it was prepared into a metallographic sample.

[0091] I. Observe whether Widmanstätten structure exists in the metallographic structure of each sample. Use the presence and absence of Widmanstätten structure as the dividing line, and take the laser power and scanning speed corresponding to the sample without Widmanstätten structure as the critical laser power P. max and critical scan rate v max .

[0092] Calculate E according to formula (1)max In the formula, P = P max v = v max D = D1, L = L1, T is the recorded printing time, and V is the volume of the cube, i.e., 10. 3 .

[0093] II. Observe whether there are pores in the metallographic structure of each sample. Use the porosity of less than or equal to 5‰ and the porosity of greater than 5‰ as the dividing line. Take the laser power and scanning speed corresponding to the sample with a porosity of less than or equal to 5‰ as the minimum acceptable laser power P. Amin and maximum acceptable scan speed v Amax .

[0094] Furthermore, P max >P Amin v max <v Amax .

[0095] (2) Import model files in formats such as STL, STP, and 3MF into the slicing software and set the corresponding printing parameters: scan line distance D1, layer thickness L1, empirical laser power P. exp and experience scan speed v exp .

[0096] (3) In the slicing software, add support to the overhanging part of the part, for example, add columnar support with a diameter of 0.3 to 0.5 mm. The addition position is at the edge of the overhanging part, and the addition interval is about 5 to 10 mm. Then slice and save.

[0097] (4) Configure the optimization method for the optimization software and set the minimum acceptable laser power P. Amin and maximum acceptable scan speed v Amax .

[0098] (5) Analyze the slice file. The part to be formed is decomposed into several printing units. Use software to analyze the proportion of the solid area in each printing unit (for example, the unit is a cuboid with a height of 3 slice heights (layer thickness), a length of 5mm, and a width of 5mm), that is, calculate the forming volume of each unit.

[0099] (6) Analyze each printing unit using software, based on the empirical laser power P. exp and experience scan speed v exp Under these conditions, determine the energy required to form the volume per unit time for each unit, denoted as E. exp ;

[0100] Calculate E according to formula (1) exp In the formula, P = P exp v = v expD = D1, L = L1, V is the forming volume of the current unit, and T is calculated according to formula (2).

[0101] For any printable cell:

[0102] If E in the printing unit exp ≤E max Then use P exp and v exp The current cell is printed using laser power and scanning speed;

[0103] If E in the printing unit exp >E max Then, by reducing the laser power and / or increasing the scanning speed, E exp ≤E max ;in,

[0104] When P Amin ≤ Adjusted final laser power < P exp And v Amax ≤ Adjusted final scan speed < v exp If the laser power and scanning speed are adjusted, the current unit will be printed.

[0105] When the final adjusted laser power < P Amin And the adjusted final scan speed > v Amax When, then P is used. Amin and v Amax The current cell is printed using the final laser power and final scanning speed, and the laser forced delay is turned off during the printing process, so that the E in the cell... exp ≤E max The extended time is determined using the following method:

[0106] Using P Amin and v Amax E is obtained from the laser power and scanning time using formula (1). max The printing time T1 is obtained by formula (2), and the extended time is T1-T2.

[0107] The methods to extend the time are as follows:

[0108] The calculated delay time is evenly distributed to each printing layer of the current unit. The delay is carried out between 25% and 75% of the printing area of ​​each printing layer, and the stopping positions of different printing layers do not overlap to ensure the flatness of the printing layers.

[0109] (7) After the above steps, the printing laser power and scanning speed of each unit were determined, and D1 and L1 were used as the scanning line distance and printing layer thickness. Then, the optimized file was saved and exported, and the corresponding unit was printed using the determined parameters of each printing unit until the part was formed.

[0110] It is understandable that the calculation process of the method of the present invention can be performed in batches using calculation software. For example, reducing the laser power can be calculated once for every 5W reduction, increasing the scanning speed can be calculated once for every 5mm / s increase, or it can be processed according to the actual situation.

[0111] In addition, the forming volume mentioned in this invention refers to the volume of the forming part, which is the volume of the forming part, excluding the raw materials (such as powders laid out) that do not need to be melted and formed during the preparation process.

[0112] To facilitate better understanding, the present invention will be further illustrated below with several specific examples, but the preparation process is not limited to these examples, and the content of the present invention is not limited to these examples.

[0113] Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.

[0114] The following examples and comparative printed parts are as follows: Figure 3 and Figure 4 As shown, the specific dimensions are as follows: Cube dimensions: length × width × height = 15mm × 10mm × 10mm; Overhanging structure dimensions: length × width × thickness = 60mm × 10mm × 4mm; The angle formed by the overhanging structure and the horizontal line is 20°; The intersection of the overhanging structure and the cube is at the middle of the long side of the cube, and 4mm below the long side; The resulting combined structure has dimensions of length × width × height = 65mm × 15mm × 16mm. The powder is spread according to the dimensions of the combined structure.

[0115] The raw material used was 17-4PH with a particle size of 17-53μm, a slice thickness of 0.06mm, a scanning line spacing of 0.11mm, an empirical laser power of 375W, and an empirical scanning speed of 1000mm / s.

[0116] Example 1

[0117] 1. Set up an orthogonal experiment to determine the critical laser power P max and critical scan rate v max :

[0118] Use drawing software to generate 10mm*10mm*10mm cubes, then import them into slicing software. Use the slicing software to assign different parameters to different cubes and print the corresponding samples. The orthogonal parameter table is shown in Table 1.

[0119] Table 1

[0120] serial number Laser power W Scanning speed mm / s 1-1 250 800 1-2 250 900 1-3 250 1000 1-4 250 1100 1-5 250 1200 1-6 300 800 1-7 300 900 1-8 300 1000 1-9 300 1100 1-10 300 1200 1-11 350 800 1-12 350 900 1-13 350 1000 1-14 350 1100 1-15 350 1200 1-16 400 800 1-17 400 900 1-18 400 1000 1-19 400 1100 1-20 400 1200 1-21 450 800 1-22 450 900 1-23 450 1000 1-24 450 1100 1-25 450 1200

[0121] Combination Figure 5 As shown, the maximum energy combination that does not produce Widmanstätten structure was found to be sample 1-22, i.e., 450W, 900mm / s. Calculations show that E... max =450*1000 / (900*0.11*0.06*6000)=12.63mm 3 ·s.

[0122] 2. Set up orthogonal experiments to determine the minimum acceptable laser power P. Amin and maximum acceptable scan speed v Amax :

[0123] Use drawing software to generate 10mm*10mm*10mm cubes, then import them into slicing software. Use the slicing software to assign different parameters to different cubes and print the corresponding samples. The orthogonal parameter table is shown in Table 2.

[0124] Table 2

[0125] serial number Laser power W Scanning speed mm / s 2-1 100 900 2-2 100 1000 2-3 100 1100 2-4 100 1200 2-5 100 1300 2-6 150 900 2-7 150 1000 2-8 150 1100 2-9 150 1200 2-10 150 1300 2-11 200 900 2-12 200 1000 2-13 200 1100 2-14 200 1200 2-15 200 1300 2-16 250 900 2-17 250 1000 2-18 250 1100 2-19 250 1200 2-20 250 1300 2-21 300 900 2-22 300 1000 2-23 300 1100 2-24 300 1200 2-25 300 1300

[0126] Combination Figure 6 As shown, calculations based on the metallographic solid area and void area revealed that when the power is less than 250W and the speed is greater than 900mm / s, the porosity is greater than 5‰. Data sets 2-16 were set as the maximum acceptable scanning speed and minimum acceptable laser power allowed during the printing process, i.e., the minimum acceptable laser power is 250W and the maximum acceptable scanning speed is 900mm / s.

[0127] 3. Import the part model into the slicing software, and add a 0.3mm diameter columnar support every 5mm, such as... Figure 7 and Figure 8 As shown, the processing parameters are set as follows: laser power 375W, scanning speed 1000mm / s.

[0128] 4. Divide the part into unit structures (cubes with a height of 3 slices (layer thickness), a length of 5mm, and a width of 5mm). Each unit starts from the lower left of the slice and is arranged in a zigzag pattern upwards to the upper right corner, resulting in a total of 140,795 unit structures. Areas that are less than one unit are merged with the previous unit.

[0129] 5. Analyze each unit. Taking one unit as an example, the total length of the scanning line in this unit is 234mm, the scanning time is 0.234s, and powder needs to be laid twice every three layers. The time for each powder laying is 8s (the parameters of the machine itself). The time for this unit is 16.234s, and the solid ratio, i.e. the forming volume, is 100%.

[0130] The energy E per unit time within this unit exp =Power used * Volume / (Scan line distance * Layer thickness * Time) = 375 * 5 * 5 * 0.06 * 3 / (0.11 * 1000 * 0.06 * 16.234) = 15.75 J / mm·s, greater than E max The value of .

[0131] Therefore, by reducing the laser power and increasing the scanning speed, when the parameters are adjusted to 250W and 900mm / s, E exp The value is 11.67, which is still higher than the set value of E. max The value of E for this unit is calculated using 250W and 900mm / s as printing parameters. exp ≤E max The completion time is at least 16.334 seconds, requiring a delay. For ease of calculation, each printed layer will have a delay of 0.04 seconds. exp The value is 11.58, which meets the requirements. Therefore, this unit is printed with 250W and 900mm / s as the printing parameters. The three printing layers are printed and paused for 0.12s at 31%, 47%, and 64% completion, respectively, to complete the printing of this unit.

[0132] In another cell, the cell body accounts for 69% of the total volume. The scan length within this cell is 163.8 mm, and the analysis time for this cell is 12.16 s. Therefore, the energy per unit time for this cell is E. exp =375*5*5*0.06*3*0.69 / (0.11*1000*0.06*12.16)=14.51J / mm 3 ·s, greater than E max Optimization is needed. The software performs calculations every 5W. The calculations show that when the laser power is reduced to 295W, E... exp It is 11.41, which is less than Emax Therefore, the unit was printed with 295W and 1000mm / s as required.

[0133] In another cell, the cell entity accounts for 2.4% of the total area. The scan length within this cell is 13.61 mm, and the analysis time for this cell is 12.01 s. Therefore, the energy per unit time for this cell is E. exp=375*5*5*0.06*3*0.024 / (0.11*1000*0.06*12.01)=0.51J / mm 3 ·s, less than E max This will not produce overheated structures, so the unit is printed with 375W and 1000mm / s as the parameters.

[0134] Following the above method, the laser power and scanning speed required for printing each unit were calculated by software. The printing took a total of 90 minutes to obtain the required parts.

[0135] Comparative Example 1

[0136] In the slicing software, add a sheet-like structure with a side length of 0.5mm, a thickness of 0.2mm, and a center thickness of 0.3mm connecting each side of the square support (forming an assembly). Place a square support assembly every 5mm (structure as follows). Figure 9 and Figure 10 As shown, the laser power was 375W and the scanning speed was 1000mm / s for printing. The printing time was 105 minutes to obtain the required parts.

[0137] Comparative Example 2

[0138] The difference from Comparative Example 1 is that the support structure used is the same as in Example 1, resulting in printing failure and warping. Figure 11 As shown.

[0139] Results Comparison

[0140] Ten measurement points were selected on the cube of the molded parts of Example 1 and Comparative Example 2 respectively to measure their hardness, and the results are shown in Table 3.

[0141] Table 3

[0142]

[0143] Combination Figure 11 and Figure 12 As shown in Table 3, the parts printed by the method of the present invention do not exhibit warping, the parts are well-formed, and the hardness value of the parts is not significantly different from that of the comparative example, thus ensuring the mechanical properties of the parts.

[0144] Furthermore, the method of the present invention and the support structure of Comparative Example 1, with the same support point locations, use a support structure with a volume of 13 mm. 3 The printing time was 90 minutes, and the removal of the support structure only took 8 minutes; while the support volume of Comparative Example 1 was as high as 1988 mm². 3The printing time was 105 minutes, and the subsequent removal of the support structure took 14 minutes.

[0145] Therefore, it can be seen that the method of the present invention can successfully print the required parts with a small number of supports, and the printing time is short, the mechanical properties can meet the requirements, the printing efficiency is high, the cost is low, and the subsequent processing is simple and quick.

[0146] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Those skilled in the art can make various modifications and refinements without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

Claims

1. A method for additive manufacturing of a metallic material, characterized in that, Includes the following steps: The scan line distance and printing layer thickness were determined, and then metal block samples were printed with different laser powers and scanning speeds. The critical laser power P was determined based on the microstructure analysis of the metal block samples. max and critical scan rate v max And determine the minimum acceptable laser power P Amin and maximum acceptable scan speed v Amax ; Among them, P max >P Amin v max <v Amax ; Under the same scan line distance and printing layer thickness, with P max and v max E represents the energy required to obtain the volume formed per unit time when printing with the same metal material, as a combination of laser power and scanning speed. max ; The part to be formed is decomposed into several printing units. Each printing unit is analyzed to determine the laser power and scanning speed corresponding to each printing unit, and the corresponding unit is printed until the part is formed. The process of analyzing the printing unit includes: Under the same scan line distance and printed layer thickness, with empirical laser power P exp and experience scan speed v exp As laser power and scanning speed, the energy of the forming volume per unit time of the printing unit is determined when printing with the same metal raw material, denoted as E. exp ; For any printable cell: If E in the printing unit exp ≤E max Then use P exp and v exp The current cell is printed using laser power and scanning speed; If E in the printing unit exp >E max Then, by reducing the laser power and / or increasing the scanning speed, E exp ≤E max ;in, When P Amin ≤ Adjusted final laser power < P exp , and v Amax ≤ Adjusted final scan speed < v exp If the laser power and scanning speed are adjusted, the current unit will be printed. When the final adjusted laser power < P Amin And the adjusted final scan speed > v Amax When, then P is used. Amin and v Amax The current cell is printed using the final laser power and final scanning speed, and the laser forced delay is turned off during the printing process, so that the E in the cell... exp ≤E max .

2. The additive manufacturing method for metallic materials according to claim 1, characterized in that, The energy of the formed volume per unit time is calculated according to formula (1): In the formula, E represents the energy of the formed volume per unit time, in J / mm². 3 •s; P is laser power, W; v is scanning speed, mm / s; D is scan line distance, mm; L is printing layer thickness, mm; T is printing time, s; V is printing volume, mm. 3 .

3. The additive manufacturing method for metallic materials according to claim 2, characterized in that, The printing time T is calculated according to formula (2): In the formula, T is the printing time (s); l is the total length of the printed layer (mm); v is the scanning speed (mm / s); t is the pause time between adjacent printed layers (s); and N is the number of printed layers.

4. The additive manufacturing method for metallic materials according to claim 3, characterized in that, The laser forced delay is turned off during the printing process, and the extended time is determined by the following method: Using P Amin and v Amax E is obtained from the laser power and scanning time using formula (1). max The printing time T1 is obtained by formula (2), and the extended time is T1-T2.

5. The additive manufacturing method for metallic materials according to claim 1, characterized in that, E in the guarantee unit exp ≤E max Under the premise of this, determine the printing extension time of the current cell and allocate it to the printing layer of the current cell for the delay.

6. The additive manufacturing method for metallic materials according to claim 5, characterized in that, Delays are assigned to the printing layer, including: The delay time is evenly distributed to each printing layer of the current unit, with a delay between 25% and 75% of the printing area of ​​each printing layer completed, and the dwell positions of different printing layers do not overlap.

7. The additive manufacturing method for metallic materials according to claim 1, characterized in that, Determine the critical laser power P max and critical scan rate v max include: The scanning line distance and printing layer thickness were determined, and metal block samples were printed using different laser powers and scanning speeds. The metallographic structure of each sample was analyzed. The presence or absence of Widmanstätten structure was used as the dividing line, and the laser power and scanning speed corresponding to the sample without Widmanstätten structure were taken as the critical laser power P. max and critical scan rate v max .

8. The additive manufacturing method for metallic materials according to claim 1, characterized in that, Determine the minimum acceptable laser power P Amin and maximum acceptable scan speed v Amax include: The scanning line distance and printing layer thickness were determined, and metal block samples were printed using different laser powers and scanning speeds. The metallographic structure of each sample was analyzed. The boundary between samples with a porosity of less than or equal to 5‰ and those with a porosity greater than 5‰ was used. The laser power and scanning speed corresponding to the samples with a porosity of less than or equal to 5‰ were taken as the minimum acceptable laser power P. Amin and maximum acceptable scan speed v Amax .

9. A method for manufacturing a metal part with a cantilever structure, characterized in that, The additive manufacturing method includes the metallic material as described in any one of claims 1-8.

10. The method for preparing a metal part with a cantilever structure according to claim 9, characterized in that, During fabrication, columnar supports with a diameter of 0.3 to 0.5 mm are set along the edge of the suspended structure, with a spacing of 5 to 10 mm between adjacent supports.

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