Additive manufacturing method of metal material

Abstract

The invention provides an additive manufacturing method of a metal material, which comprises the following steps of: unitizing part printing, dynamically adjusting the printing unit energy of each unit, controlling the printing unit energy to be within critical unit energy, and controlling the energy density input in unit time to be within a proper range during printing, so that the printing unit energy can be controlled to be within the critical unit energy; according to the method, the overheat phenomenon is avoided, buckling deformation caused by overlarge internal residual stress is avoided, the part forming quality is good, the mechanical property of the formed part is guaranteed, meanwhile, the printing efficiency is improved, and the cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of additive manufacturing, and in particular to an additive manufacturing method for metal materials. Background Art

[0002] Laser powder bed fusion (LPBF) is an advanced metal additive manufacturing technology that uses a high-energy laser beam to melt metal powder layer by layer and build complex metal parts by stacking them layer by layer. LPBF technology not only has the characteristics of high precision and high quality, but also can directly manufacture parts with optimized internal structures and complex geometric shapes, greatly meeting the needs of aerospace, automotive manufacturing and other fields for high-performance metal parts. At the same time, LPBF technology also has the advantages of high material utilization and short production cycle, which has brought revolutionary changes to modern manufacturing.

[0003] In the LPBF process, for some thin plate structures that are at 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 required to ensure the heat dissipation of the parts and prevent the parts from collapsing. However, the addition of supports will increase manufacturing time, material waste, and the difficulty of post-processing. If the added supports are reduced, the parts will overheat and warp. This is because after each layer of printing is completed, some areas are in contact with metal powder, and the thermal conductivity of metal powder is lower than that of the metal entity. Therefore, during the printing process, the energy of the areas in contact with the metal powder will accumulate, and the accumulated heat will cause overheating, which will eventually cause the parts to overheat, warp, and deform, and fail to form.

[0004] In order to solve the problem of part deformation caused by reducing support parts when printing low-angle parts, researchers have tried to improve it through topological structure optimization. For example, Dong Yongjia et al. proposed a new topological optimization method. Under the framework of density-based topological optimization, this method considers the support constraints in additive manufacturing and reduces the volume of the support structure through mathematical models and algorithms; Wu Shuting et al. proposed the constraints and design rules for lightweight design of parts based on SLM technology. Taking a certain type of satellite radiator as an example, finite element analysis and topological optimization design were carried out, and the weight was reduced and the performance was improved by optimizing the structure. Although this method solves some problems through structural optimization, the structure of some parts is already optimal or cannot be optimized due to certain circumstances.

[0005] In addition, researchers have also tried to solve the overheating problem that occurs during small-angle printing by optimizing the process. For example, the Chinese patent publication number CN117182106A discloses a support-free laser selective melting additive manufacturing method, which pre-sinters the first layer and then sinters the entity, repeats 1-20 layers, and then prints the entity. Although this method can reduce support, it may cause pores during the first sintering process. The pores are not eliminated during the second sintering process, which results in defects and requires repeated scanning, resulting in long printing time and low efficiency.

[0006] For example, the SLM unsupported forming method of a superalloy cross-section mutation structure disclosed in the Chinese patent publication number CN114406286A adopts a small energy density to realize the unsupported planar overhang structure of the superalloy. Although the process optimization method of reducing a certain part of the energy avoids the occurrence of overheating, the reduction in energy leads to an increase in porosity and a decrease in mechanical properties.

[0007] In the additive manufacturing process of metal materials, how to avoid the warping and deformation of parts is still a difficult problem to solve. Although the existing technology attempts to solve the problems of stress concentration and part warping and deformation caused by overheating through topological structure optimization and energy density optimization, it is still not ideal. Summary of the invention

[0008] The purpose of the present invention is to address the deficiencies in the prior art and provide an additive manufacturing method for metal materials, which unitizes the printing of parts and dynamically adjusts the printing unit energy of each unit. By adjusting the energy per unit volume, the energy density input per unit time is within an appropriate range, thereby avoiding overheating and warping caused by excessive internal residual stress. The part forming quality is good, and the mechanical properties of the formed parts are guaranteed, while the printing efficiency is improved and the cost is reduced.

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

[0010] Determine the scanning line distance and printing layer thickness, then print the metal block sample at different laser powers and scanning speeds, and determine the critical laser power P based on the microstructure analysis of the metal block sample. max and critical scanning speed v max , and determine the minimum acceptable laser power P Amin and the maximum acceptable scanning speed v Amax ; Among them, P max >P Amin , v max <v Amax ;

[0011] Under the same scanning line distance and printing layer thickness conditions, P max and v max As the laser power and scanning speed, the energy of the formed volume per unit time when printing with the same metal raw material is obtained, which is recorded as E max ;

[0012] Decompose the part to be formed into several printing units, analyze each printing unit, determine the laser power and scanning speed corresponding to each printing unit, and print the corresponding unit until the part is formed;

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

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

[0015] For any print unit:

[0016] If the E in the print unit exp ≤E max , then use P exp and v exp Print the current unit as laser power and scan speed;

[0017] If the E in the print 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 scanning speed<v exp When , the adjusted laser power and scanning speed are used to print the current unit;

[0019] When the final laser power is adjusted < P Amin , and the final scanning speed adjusted is >v Amax When P Amin and v Amax Print the current unit as the final laser power and final scanning speed, and turn off the laser forced delay during printing, so that the E in the unit exp ≤E max .

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

[0021]

[0022] Where E is the energy of the forming volume per unit time, J / mm 3 ·s; P is laser power, W; v is scanning speed, mm / s; D is scanning 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] Where, 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; N is the number of printed layers.

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

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

[0028] As an optional implementation, in the guarantee unit E exp ≤E max Under the premise of , the printing extension time of the current unit is determined, and the printing layer of the current unit is allocated for delay.

[0029] As an optional implementation, allocating to a printing layer for delay includes:

[0030] The extended time is evenly distributed to each printing layer of the current unit, and the delay is performed when the printing area of ​​each printing layer is 25-75% completed, and the stop positions of different printing layers do not overlap.

[0031] As an optional embodiment, the critical laser power P is determined max and critical scanning speed v max include:

[0032] Determine the scanning line distance and printing layer thickness, use different laser powers and scanning speeds to print metal block samples, analyze the metallographic structure of each sample, and use the presence of Widmanstatten structure and the absence of Widmanstatten structure in the structure as the boundary. Take the laser power and scanning speed corresponding to the sample without Widmanstatten structure as the critical laser power P max and critical scanning speed v max .

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

[0034] Determine the scanning line distance and printing layer thickness, use different laser powers and scanning speeds to print metal block samples, analyze the metallographic structure of each sample, and use the porosity of the tissue less than or equal to 5‰ and the porosity greater than 5‰ as the boundary. 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 the maximum acceptable scanning speed v Amax .

[0035] According to a second aspect of the present invention, there is provided a method for preparing a metal part having an overhang structure, comprising the additive manufacturing method of the metal material according to any one of claims 1 to 8.

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

[0037] It can be seen from the above technical solution of the present invention that the additive manufacturing method of metal materials proposed in the present invention unitizes the part printing 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 to be within an appropriate range during printing, overheating is avoided, and warping deformation caused by excessive internal residual stress is avoided. The part forming quality is good, and the mechanical properties of the formed parts are guaranteed. At the same time, the printing efficiency is improved, the subsequent processing is simple, and the cost is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 Schematic diagram of a hanging structure having an angle with a horizontal plane in an example of the present invention.

[0039] Figure 2 It is a process flow chart of the additive manufacturing method of the metal material of the present invention.

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

[0041] Figure 5 The critical laser power P is determined in Example 1 of the present invention. max and critical scanning speed v max The metallographic structure diagram of the corresponding sample.

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

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

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

[0045] Fig.11 It is a printed physical picture of the parts of comparative example 2 of the present invention.

[0046] Fig.12 It is a printed physical picture of the parts of Example 1 of the present invention. DETAILED DESCRIPTION

[0047] In order 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 present invention are described in this disclosure with reference to the accompanying drawings, in which many illustrative embodiments are shown. The embodiments of the present disclosure are not necessarily intended to include all aspects of the present invention. It should be understood that the various concepts and embodiments introduced above, as well as those described in more detail below, can be implemented in any of many ways.

[0049] Combination Figure 1As shown, taking the use of laser powder bed melting technology to print a hanging structure with an angle (α) with the horizontal plane as an example, powder printing is performed on a substrate 1. Due to the existence of the hanging 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 next layer of powder at this powder position needs to be melted and deposited, so that the print will form a solid part and a powder part 2, and the hanging structure will have three situations, namely, the area without parts in the upper layer in the Z direction is called the upper surface 3; the area without parts in the lower layer in the Z direction is called the lower surface 4; and all surfaces except the upper and lower surfaces are called inner surfaces 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 area of ​​the current layer. Therefore, if the printing heat is too high, too much heat will accumulate in the lower surface area, which will eventually lead to defects such as part warping and deformation.

[0051] Therefore, the present invention constructs a dynamic energy adjustment strategy that reduces the energy input into the high-energy area during the part printing process without changing the energy area of ​​the low stress area, so as to judge the input energy density per unit time. If it is too high, it will be adjusted to reduce the energy input into the high-energy area without changing the energy area of ​​the low stress area. This can achieve no increase or even reduction in printing time, and at the same time, there is no need to reduce too much energy to ensure the mechanical properties of the parts.

[0052] It can be understood that the method of the present invention is applicable to additive manufacturing of metal materials using high-energy heat sources, for example, 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, a method for additive manufacturing of metal materials is provided, comprising the following steps:

[0054] Determine the scanning line distance and printing layer thickness, then print the metal block sample at different laser powers and scanning speeds, and determine the critical laser power P based on the microstructure analysis of the metal block sample. max and critical scanning speed v max , and determine the minimum acceptable laser power P Amin and the maximum acceptable scanning speed v Amax ; Among them, P max >P Amin , v max <v Amax .

[0055] As an optional example, determine the critical laser power P max and critical scanning speed v maxinclude:

[0056] Determine the scanning line distance and printing layer thickness, use different laser powers and scanning speeds to print metal block samples, analyze the metallographic structure of each sample, and use the presence of Widmanstatten structure and the absence of Widmanstatten structure in the structure as the boundary. Take the laser power and scanning speed corresponding to the sample without Widmanstatten structure as the critical laser power P max and critical scanning speed v max .

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

[0058] Determine the scanning line distance and printing layer thickness, use different laser powers and scanning speeds to print metal block samples, analyze the metallographic structure of each sample, and use the porosity of the tissue less than or equal to 5‰ and the porosity greater than 5‰ as the boundary. 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 the maximum acceptable scanning speed v Amax .

[0059] As a preferred example, an orthogonal test can be used to determine the critical laser power P max and critical scanning speed v max , and the minimum acceptable laser power P Amin and the maximum acceptable scanning speed v Amax It is understandable that one set of orthogonal experiments can be set to obtain the above four parameters at the same time, or two sets of orthogonal experiments can be set to obtain the critical laser power P respectively. max and critical scanning speed v max , and the minimum acceptable laser power P Amin and the maximum acceptable scanning speed v Amax .

[0060] Afterwards, under the same scanning line distance and printing layer thickness conditions, the P max and v max As the laser power and scanning speed, the energy of the formed volume per unit time when printing with the same metal raw material is obtained, which is recorded as E max .

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

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

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

[0064] For any print unit:

[0065] If the E in the print unit exp ≤E max , then use P exp and v exp Print the current unit as laser power and scan speed;

[0066] If the E in the print 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 scanning speed<v exp When , the adjusted laser power and scanning speed are used to print the current unit;

[0068] When the final laser power is adjusted < P Amin , and the final scanning speed adjusted is >v Amax When P Amin and v Amax Print the current unit as the final laser power and final scanning speed, and turn off the laser forced delay during printing, so that the E in the unit exp ≤E max .

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

[0070] First determine the print layer thickness. The common print 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; and for prints that require higher time, you can choose a layer thickness of 0.3mm or thicker.

[0071] After determining the printing layer thickness, determine the laser power that can completely melt the metal raw material under the layer thickness according to the layer thickness and the type of raw material. Generally speaking, the energy density of metals with high melting points is definitely greater than that of metals with low melting points. For example, at a layer thickness of 0.06mm, stainless steel may require 400W to be completely melted, titanium alloy / aluminum alloy generally requires more than 200W, and although the melting point of copper alloy is not high, due to the difference in light absorption, it also requires a higher power of 400W to melt; single-channel tests can be performed at different laser powers, and multi-channel tests can be performed using the laser power that completely fuses a single channel, and the scanning line distance that forms a plane between two adjacent channels is used to determine the required scanning line distance.

[0072] Afterwards, the block sample is printed at the above-determined scanning line distance and printing layer thickness, and the laser power and scanning speed corresponding to the sample with low surface roughness are used as the empirical laser power P exp and the empirical scanning speed v exp .

[0073] It is understandable that the scanning line distance, printing layer, and empirical laser power P exp and the empirical scanning speed v exp It can be determined according to the above method, or the commonly used production parameters can be directly adopted. Each enterprise has its own commonly used production parameters, and the empirical values ​​can be directly adopted, or the parameters recorded in the literature can be directly adopted.

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

[0075]

[0076] Where E is the forming volume per unit time, J / mm 3 ·s; P is laser power, W; v is scanning speed, mm / s; D is scanning 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] Where, 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; N is the number of printed layers.

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

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

[0082] As an optional example, in the guarantee unit E exp ≤E max Under the premise of , the printing extension time of the current unit is determined, and the printing layer of the current unit is allocated for delay.

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

[0084] The extended time is evenly distributed to each printing layer of the current unit, and the delay is performed when the printing area of ​​each printing layer is 25-75% completed, and the stop positions of different printing layers do not overlap.

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

[0086] As an optional example, during preparation, columnar support members with a diameter of 0.3 to 0.5 mm are arranged along the edge of the overhanging structure, and the interval between adjacent support members is 5 to 10 mm.

[0087] In one typical example, the aforementioned additive manufacturing method of metal materials is used to print parts with overhanging structures by laser powder bed melting technology. The manufacturing process includes the following specific steps:

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

[0089] Determine the scanning line distance D1 and printing layer thickness L1 required for printing parts, design orthogonal experiments with different laser powers and different scanning speeds, and use powder spreading to print the corresponding metal samples. The sample is a cube with a side length of 10 mm, and record the printing process time.

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

[0091] Ⅰ. Observe whether there is Widmanstatten structure in the metallographic structure of each sample, and take the laser power and scanning speed corresponding to the sample without Widmanstatten structure as the boundary. max and critical scanning speed v max .

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

[0093] Ⅱ. Observe whether there are pores in the metallographic structure of each sample, and take the porosity of the tissue less than or equal to 5‰ and the porosity greater than 5‰ as the boundary. 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 the maximum acceptable scanning speed v Amax .

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

[0095] (2) Import the model files in stl, stp, 3mf and other formats into the slicing software and set the corresponding printing parameters: scanning line distance D1, layer thickness L1, empirical laser power P exp and the empirical scanning speed v exp .

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

[0097] (4) Set the optimization mode of the optimization software and set the minimum acceptable laser power P Amin and the maximum acceptable scanning speed v Amax .

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

[0099] (6) Use software to analyze each printing unit, and then use the empirical laser power P exp and the empirical scanning speed v exp Under these conditions, the energy of the forming volume per unit time of each unit is determined, which is recorded as E exp ;

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

[0101] For any print unit:

[0102] If the E in the print unit exp ≤E max , then use P exp and v exp Print the current unit as laser power and scan speed;

[0103] If the E in the print 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 scanning speed<v exp When , the adjusted laser power and scanning speed are used to print the current unit;

[0105] When the final laser power is adjusted < P Amin , and the final scanning speed adjusted is >v Amax When P Amin and v Amax Print the current unit as the final laser power and final scanning speed, and turn off the laser forced delay during printing, so that the E in the unit exp ≤E max ; The extended time is determined by the following method:

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

[0107] Here are some ways to extend the time:

[0108] The calculated extension time is evenly distributed to each printing layer of the current unit, and the delay is performed when the printing area of ​​each printing layer is 25-75% completed, and the stop positions of different printing layers do not overlap to ensure the flatness of the printing layer.

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

[0110] It can be understood that the calculation process of the method of the present invention can be calculated in batches using calculation software. For example, reducing the laser power can be calculated once every time it is reduced by 5W, and increasing the scanning speed can be calculated once every time it is increased by 5mm / s, or it can be processed based on actual conditions.

[0111] In addition, the forming volume mentioned in the present invention refers to the raw materials (such as laid powder) that do not need to be melted and formed during the preparation process, but will exist in the forming part during the preparation process. However, these raw materials do not belong to the volume used for calculation. Therefore, the forming volume refers to the volume of the forming part and does not include raw materials that have not formed a solid body.

[0112] For better understanding, the present invention is further described below in conjunction with several specific examples, but the preparation process is not limited thereto, and the content of the present invention is not limited thereto.

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

[0114] The parts printed in the following embodiments and comparative examples are as follows: Figure 3 and Figure 4 As shown, the specific dimensions are: cube size: length × width × height = 15mm × 10mm × 10mm, overhang structure size: length × width × thickness = 60mm × 10mm × 4mm, the angle formed by the overhang structure and the horizontal line is 20°, and the intersection of the overhang structure and the cube is in the middle of the long side of the cube and 4mm below the long side; the size of the assembly thus formed is length × width × height = 65mm × 15mm × 16mm, and the powder is applied according to the size of the assembly.

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

[0116] Example 1

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

[0118] Use drawing software to generate a 10mm*10mm*10mm cube, then import it into the 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 in the figure, it is found that the maximum energy combination that does not produce Widmanstatten structure is sample 1-22, that is, 450W, 900mm / s. After calculation, it can be obtained that E max =450*1000 / (900*0.11*0.06*6000)=12.63mm 3 ·s.

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

[0123] Use drawing software to generate a 10mm*10mm*10mm cube, then import it into the 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, through the calculation of metallographic entity area and void area, it was found that when the power is less than 250W and the speed is greater than 900mm / s, the void ratio is greater than 5‰, and the data of groups 2-16 are set as the maximum acceptable scanning speed and minimum acceptable laser power allowed during the printing process, that is, 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 columnar support with a diameter of 0.3mm every 5mm. 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 (rectangles with a height of 3 slice heights (layer thickness), a length of 5 mm, and a width of 5 mm). Each unit starts from the lower left corner of the slice and is arranged in a zigzag pattern upward to the upper right corner. A total of 140,795 unit structures are divided, and the area with less than one unit is merged with the previous unit.

[0129] 5. Analyze each unit. Take one of the units as an example. The scanning line length in this unit is 234mm, and the scanning time is 0.234s. Every three layers need to be spread powder twice, and the time for each powder spreading is 8s (the parameter of the machine itself). The time taken for this unit is 16.234s, and the solid proportion, that is, the forming volume, is 100%.

[0130] The energy per unit time in this unit is E 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, the laser power was reduced and the scanning speed was increased. When the parameters were adjusted to 250W and 900mm / s, E exp It is 11.67, still higher than the set E max At this time, with 250W and 900mm / s as the printing parameters, calculate the unit E exp ≤E max The completion time is at least 16.334s, and a delay is required. For the convenience of calculation, the delay for each printing layer is 0.04s. exp The value is 11.58, which meets the requirements. Therefore, the unit uses 250W and 900mm / s as printing parameters. The three printing layers stay at 31%, 47%, and 64% respectively for 0.12s to complete the printing of this unit.

[0132] In another unit, the unit entity accounts for 69%, the scanning length in the unit is 163.8mm, and the completion time of the analysis unit is 12.16s, so the energy per unit time of the unit 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 , needs to be optimized, and the software is used to calculate every 5W. After calculation, it is found that when the laser power is reduced to 295W, E exp is 11.41, which is less than Emax Therefore, the unit takes 295W and 1000mm / s as printing parameters.

[0133] In another unit, the unit entity accounts for 2.4%, the scanning length in this unit is 13.61mm, and the completion time of this analysis unit is 12.01s, so the energy per unit time of this unit 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 , no overheating will occur, therefore, the unit uses 375W and 1000mm / s as printing parameters.

[0134] According to the above method, the software calculates the laser power and scanning speed required for printing each unit. The printing takes a total of 90 minutes to obtain the required parts.

[0135] Comparative Example 1

[0136] In the slicing software, add a normal side length of 0.5mm, a thickness of 0.2mm, and a 0.3mm thick sheet structure in the center to connect each side of the square support (together forming a combination), and place a square support combination every 5mm (structure as shown Fig. 9 and Fig.10 As shown in the figure, the laser power is 375W and the scanning speed is 1000mm / s. The printing takes 105min to obtain the required parts.

[0137] Comparative Example 2

[0138] The difference from Comparative Example 1 is that the support body used is the support structure in Example 1, and printing fails and warping occurs, such as Fig.11 shown.

[0139] Results comparison

[0140] Ten measuring points were selected on the cubes of the formed parts of Example 1 and Comparative Example 2 to measure their hardness. The results are shown in Table 3.

[0141] Table 3

[0142]

[0143] Combination Fig.11 and Fig.12 As shown in Table 3, the parts printed by the method of the present invention do not show warping, the parts are formed, and the hardness value of the parts is not much different from that of the control example, which ensures the mechanical properties of the parts.

[0144] In addition, the volume of the support structure used in the method of the present invention and the support structure of comparative example 1 is 13 mm when the support points are the same. 3 The printing time is 90 minutes, and it only takes 8 minutes to remove the support structure later; while the support volume of comparative example 1 is as high as 1988mm 3The printing time is 105 minutes, and it takes 14 minutes to remove the support structure.

[0145] It can be seen that the method of the present invention can successfully print the required parts under the condition of a small amount of support, and the printing time is short, the mechanical properties can also meet the requirements, the printing efficiency is high, the cost is low, and the subsequent processing is simple and quick.

[0146] Although the present invention has been disclosed as above with preferred embodiments, it is not intended to limit the present invention. A person with ordinary knowledge in the technical field to which the present invention belongs may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be determined by the definition of the claims.

Claims

1. A method for additive manufacturing of metal materials, characterized in that: The following steps are involved: Determine the scanning line distance and printing layer thickness, then print the metal block sample at different laser powers and scanning speeds, and determine the critical laser power P according to the microstructure analysis of the metal block sample. max and critical scanning speed v max , and determine the minimum acceptable laser power P Amin and the maximum acceptable scanning speed v Amax ; Among them, P max >P Amin , v max <v Amax ; Under the same scanning line distance and printing layer thickness conditions, P max and v max As the laser power and scanning speed, the energy of the formed volume per unit time when printing with the same metal raw material is obtained, which is recorded as E max ; Decompose the part to be formed into several printing units, analyze each printing unit, determine the laser power and scanning speed corresponding to each printing unit, and print the corresponding unit until the part is formed; The process of analyzing the printing unit includes: Under the same scanning line distance and printing layer thickness conditions, the empirical laser power P exp and the empirical scanning speed v exp As the laser power and scanning speed, the energy of the forming volume per unit time of the printing unit when printing with the same metal raw material is determined, which is recorded as E exp ; For any print unit: If the E in the print unit exp ≤E max , then use P exp and v exp Print the current unit as laser power and scan speed; If the E in the print 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 scanning speed<v exp When , the adjusted laser power and scanning speed are used to print the current unit; When the final laser power is adjusted < P Amin , and the final scanning speed adjusted is >v Amax When P Amin and v Amax Print the current unit as the final laser power and final scanning speed, and turn off the laser forced delay during printing, so that the E in the unit exp ≤E max .

2. The additive manufacturing method of metal material according to claim 1, characterized in that: The energy of the formed volume per unit time is calculated according to formula (1): Where E is the energy of the forming volume per unit time, J / mm 3 ·s; P is laser power, W; v is scanning speed, mm / s; D is scanning 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 of metal material according to claim 2, characterized in that: The printing time T is calculated according to formula (2): Where, 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; N is the number of printed layers.

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

5. The additive manufacturing method of metal material according to claim 1, characterized in that: E in the guarantee unit exp ≤E max Under the premise of , the printing extension time of the current unit is determined, and the printing layer of the current unit is allocated for delay.

6. The additive manufacturing method of metal material according to claim 5, characterized in that: Assign to the printing layer for delay, including: The extended time is evenly distributed to each printing layer of the current unit, and the delay is performed when the printing area of ​​each printing layer is 25-75% completed, and the stop positions of different printing layers do not overlap.

7. The additive manufacturing method of metal material according to claim 1, characterized in that: Determine the critical laser power P max and critical scanning speed v max include: Determine the scanning line distance and printing layer thickness, use different laser powers and scanning speeds to print metal block samples, analyze the metallographic structure of each sample, and use the presence of Widmanstatten structure and the absence of Widmanstatten structure in the structure as the boundary. Take the laser power and scanning speed corresponding to the sample without Widmanstatten structure as the critical laser power P max and critical scanning speed v max .

8. The additive manufacturing method of metal material according to claim 1, characterized in that: Determine the minimum acceptable laser power P Amin and the maximum acceptable scanning speed v Amax include: Determine the scanning line distance and printing layer thickness, use different laser powers and scanning speeds to print metal block samples, analyze the metallographic structure of each sample, and use the porosity of the tissue less than or equal to 5‰ and the porosity greater than 5‰ as the boundary. 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 the maximum acceptable scanning speed v Amax .

9. A method for preparing a metal part with a suspension structure, characterized in that: A method for additive manufacturing of a metal material comprising the steps of claim 1 .

10. The method for preparing a metal part with a suspension structure according to claim 9, characterized in that: During preparation, columnar support members with a diameter of 0.3 to 0.5 mm are arranged along the edge of the overhanging structure, and the interval between adjacent support members is 5 to 10 mm.

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