Low cost high speed selective laser melting of titanium alloy forming method

Abstract

The application discloses a low-cost high-speed selective laser melting titanium alloy forming method, comprising the following steps: adjusting a laser to reduce a laser spot diameter; using a large layer thickness powder laying; through a single pass scanning test, a laser scanning power, speed and a melt channel width, melt channel depth relationship matrix under a set layer thickness is established; according to the matrix, the laser scanning power, speed and scanning spacing are determined according to the melt channel depth being not less than the powder thickness multiplied by the titanium alloy theoretical density and the powder bulk density ratio of 1.1 times, and scanning is started; after the scanning is finished, the platform is lowered, the powder laying scraper lays the powder on the lowered powder bed, and the laser scanning is carried out after the powder laying is rotated counterclockwise at a certain angle; the platform lowering, powder laying and laser scanning process are repeated until the part forming is completed, the part with the density exceeding 99.0% is obtained, and the forming efficiency exceeds 30 cm 3 / hour. The application can overcome the defects of low efficiency and high cost of multiple lasers, and realize the rapid forming of high-density titanium alloy parts.

Description

TECHNICAL FIELD

[0001] The application relates to a low-cost high-speed selective laser melting titanium alloy forming method and belongs to the field of additive manufacturing and advanced manufacturing. BACKGROUND

[0002] Selective laser melting is a near-net shaping method in which a digital model of an entity is sliced and discretized, and a focused laser beam is controlled to scan a powder layer point by point and layer by layer according to the discretized scanning path to accumulate a formed entity by melting and solidification. This method can melt metal powder to obtain a formed part with high density, high dimensional accuracy, good surface quality and excellent performance, and is the most promising and widely applied development direction in the fields of additive manufacturing and advanced manufacturing.

[0003] The main problem of selective laser melting is that the forming efficiency is too low. At present, the powder layer thickness is usually set to be 20-80 microns during selective laser melting forming, a laser with a spot diameter of about 100 microns is used, and the scanning speed is generally about 1000 mm / s and the scanning pitch is between 0.06 mm and 0.12 mm. The forming efficiency is only 3 cm 3 / hour-10 cm 3 / hour, which seriously affects the further application of selective laser melting.

[0004] At present, during the selective laser melting forming process, a 1064 nm fiber laser with a power of not more than 500 W is generally used, a heat conduction molten pool is formed during forming, and the forming efficiency of selective laser melting is usually improved by increasing the number of lasers. For example, Chinese invention patent application CN201811416721.5 discloses a double-beam selective laser melting additive manufacturing method, which improves the forming efficiency of selective laser melting through the synergistic effect of double laser beams; Chinese invention patent application CN201911287875.3 discloses a high-precision and high-efficiency double-beam composite laser selective melting forming method and device, which uses two laser beams to emit light at different times or simultaneously to improve the forming efficiency; Chinese invention patent application CN202310131011.2 discloses a large-format high-efficiency high-precision laser selective melting forming equipment and method, which uses multiple laser processing units, each of which can simultaneously use multiple groups of kilowatt-level high-power lasers / hundred-watt-level high-power lasers to cooperatively form a corresponding metal powder layer sub-region, thereby improving the selective laser melting forming efficiency and expanding the forming area. However, increasing the number of lasers leads to an increase in equipment cost.

[0005] With the development of laser manufacturing technology, it is very convenient to adjust the output laser spot diameter. When the laser spot diameter is focused to within 50 microns, the laser energy density in the spot is high, and when it acts on the titanium alloy powder bed surface, it is easy to form a spoon-shaped molten pool with a large molten channel depth.

[0006] The application discloses a method for improving forming efficiency of selective laser melting titanium alloy by using a large-melting-channel-depth keyhole molten pool, and solves the problem of high cost of improving forming efficiency by multiple lasers. 3 The forming efficiency of the selective laser melting titanium alloy is improved to more than 30 cm SUMMARY

[0007] In order to solve the problems in the prior art, the application provides a low-cost high-speed selective laser melting titanium alloy forming method, which comprises the following steps:

[0008] (1) Adjust the laser, and focus the laser beam spot diameter to 30-50 mu m.

[0009] (2) Set the powder laying thickness to 180-240 mu m.

[0010] (3) Through a multi-layer single-channel scanning test, a relationship matrix of laser scanning power, scanning speed and melting channel width and melting channel depth is established, and the laser scanning power and scanning speed required for realizing the keyhole melting mode and the corresponding melting channel width and melting channel depth are determined.

[0011] (4) According to the relationship matrix of laser scanning power, scanning speed and melting channel width and melting channel depth obtained through the single-channel scanning test, the laser scanning power and scanning speed are determined according to the condition that the melting channel depth is not less than 1.1 times the product of the powder laying thickness, the theoretical density of titanium alloy and the powder accumulation density ratio; when multiple scanning power and scanning speed combinations can meet the melting channel depth requirement, the process parameter combination with the fast scanning speed is preferentially selected.

[0012] (5) After the laser scanning power and scanning speed are determined, the scanning interval is determined according to 0.4-0.5 times the melting channel width according to the single-channel scanning test melting channel width result.

[0013] (6) After laser scanning of one layer is completed, the platform is lowered, and the lowering height is equal to the product of the set powder laying thickness, the powder accumulation density and the theoretical density of titanium alloy.

[0014] (7) The powder laying scraper lays powder on the lowered powder bed on the platform.

[0015] (8) The laser scanning angle is counterclockwise rotated by 33-66 degrees, and scanning is performed.

[0016] (9) Steps 7 and 8 are repeated until the forming of the part is completed, the powder bed is cleaned, and the dense part is obtained.

[0017] Preferably, in step (2), the powder used is titanium alloy spherical powder with a maximum particle size of less than 60 μm.

[0018] Preferably, in step (3), the number of layers in the multi-layer single-pass test is 40, and the width and depth of the molten bead are determined by measuring the width of the molten area of the top layer of the molten bead and the depth of the overlapping bead in the cross-section of the formed sample by quantitative metallographic method.

[0019] Preferably, in step (9), the density of the obtained part is more than 99.0%, and the forming efficiency is more than 30 cm 3 / / hour.

[0020] Preferably, a single laser is used, and the wavelength of the laser is 1064 nm, and the power is not more than 500 W.

[0021] Advantages of the present application

[0022] (1) The present application improves the efficiency of selective laser melting to more than 30 cm 3 / hour without increasing the number of lasers and the cost of equipment, and the density of the obtained formed part is more than 99.0%, which is 3-10 times the efficiency of the common single laser selective laser forming, greatly reducing the cost of the selective laser melting formed part on the basis of improving the efficiency.

[0023] (2) In the present application, step (4) is provided to ensure good bonding, and the depth of the molten bead must be not less than 1.1 times the actual powder layer thickness; due to the shrinkage of the powder after solidification, the actual powder thickness is greater than the set powder thickness, which is the product of the set powder thickness, the theoretical density of the titanium alloy, and the ratio of the powder bulk density.

[0024] (3) Since the cross-sectional shape of the molten pool is parabolic, the measured width of the molten bead is the maximum size of the cross-section of the molten pool, and in order to ensure good overlap of the molten pool, the scanning pitch must be set to 0.4-0.5 times the width of the molten bead.

[0025] (4) The three steps of steps (3)-(5) can quickly and accurately obtain the forming process parameters. DETAILED DESCRIPTION

[0026] The technical solutions of the present application will be further described through specific embodiments. However, the following examples are only simple examples of the present application, and do not represent or limit the protection scope of the present application, and the protection scope of the present application is subject to the claims.

[0027] Example 1

[0028] A low-cost high-speed selective laser melting titanium alloy forming method, comprising the following steps:

[0029] (1) Adjust the laser with wavelength 1064 nm and output power not more than 500 W, and focus the laser beam spot diameter to 30 μm.

[0030] (2) Use TC4 titanium alloy spherical titanium powder with particle size range 15-53 μm, average particle size 39 μm, and bulk density 2.67 g / cm, and set the powder laying thickness to 240 μm.

[0031] (3) Through 40-layer single-channel scanning tests, establish the laser scanning power, scanning speed, and the relationship matrix of the melt width and the melt depth, wherein the melt width (melt width) and the melt depth (melt depth) are determined by measuring the melting area width and the overlap weld depth of the top layer melt of the formed sample cross section by quantitative metallographic method, and the required laser scanning power and scanning speed for realizing the keyhole melting mode and their corresponding melt width and depth are determined, as shown in the following table:

[0032]

[0033]

[0034] (4) According to the relationship matrix between the laser scanning power, scanning speed, and the melt width and the melt depth obtained by the single-channel scanning test, the laser scanning power is determined to be 170 W, the scanning speed is determined to be 500 mm / s, the corresponding melt width is determined to be 190 μm, and the depth is determined to be 446 μm, according to the melt depth not less than 1.1 times the product of the powder laying thickness and the ratio of the theoretical density of the titanium alloy to the powder bulk density.

[0035] (5) After the laser scanning power and the scanning speed are determined, according to the melt width result of the single-channel scanning test, the scanning pitch is determined to be 95 μm according to 0.5 times the melt width.

[0036] (6) After the laser scanning of one layer is completed, the platform is lowered, and the lowering height is equal to the product of the set powder laying thickness and the ratio of the powder bulk density to the theoretical density of the titanium alloy.

[0037] (7) The powder laying scraper lays the powder on the lowered powder bed on the platform.

[0038] (8) The laser scanning angle is counterclockwise rotated by 66°, and scanning is performed.

[0039] (9) Repeat steps 7 and 8 until the forming of the part is completed, clean the powder bed, obtain a dense part, and the forming efficiency is 41.0 cm 3 / hour, and after detection, the sample density is 99.6%.

[0040] Example 2

[0041] (1) Adjust the laser with wavelength 1064 nm and output power not more than 500 W, and focus the laser beam spot diameter to 50 μm.

[0042] (2) The TC4 titanium alloy spherical titanium powder with a particle size range of 15-55 μm, an average particle size of 32 μm, and a bulk density of 2.72 g / cm3 is used, and the powder laying thickness is set to 180 μm.

[0043] (3) Through the 40-layer single-channel scanning test, the relationship matrix of laser scanning power, scanning speed, and melt width, melt depth is established, wherein the melt width (melt width) and the melt depth (melt depth) are determined by measuring the melting area width and the overlap weld depth of the top layer of the melt of the formed sample cross section by quantitative metallographic method, and the laser scanning power and scanning speed required to realize the keyhole melting mode and their corresponding melt width and depth are determined, as shown in the following table:

[0044]

[0045] (4) According to the relationship matrix of laser scanning power, scanning speed, and melt width, melt depth obtained by the single-channel scanning test, under the condition that the melt depth is not less than 1.1 times the product of the powder laying thickness and the ratio of the theoretical density of the titanium alloy to the powder bulk density, the process parameter combination with fast scanning speed is preferentially selected to determine that the laser scanning power is 170 W, the scanning speed is 600 mm / s, the corresponding melt width is 220 μm, and the depth is 408 μm.

[0046] (5) After the laser scanning power and scanning speed are determined, according to the melt width result of the single-channel scanning test, the scanning pitch is determined to be 88 μm according to 0.4 times the melt width.

[0047] (6) After the laser scanning of one layer is completed, the platform is lowered, and the lowering height is equal to the product of the set powder laying thickness and the ratio of the powder bulk density to the theoretical density of the titanium alloy.

[0048] (7) The powder laying scraper lays the powder on the lowered powder bed on the platform.

[0049] (8) The laser scanning angle is counterclockwise rotated by 33°, and scanning is performed.

[0050] (9) Steps 7 and 8 are repeated until the forming of the part is completed, the powder bed is cleaned, and a dense part is obtained, and the forming efficiency is 34.2 cm 3 / hour. After detection, the sample density is 99.3%.

[0051] Example 3

[0052] (1) The laser with a wavelength of 1064 nm and an output power of not more than 500 W is adjusted, and the laser beam spot diameter is focused to 40 μm.

[0053] (2) The TA1 titanium alloy spherical titanium powder with a particle size range of 15-60 μm, an average particle size of 34 μm, and a bulk density of 2.86 g / cm3 is used, and the powder laying thickness is set to 240 μm.

[0054] (3) Through the 40-layer single-channel scanning test, a laser scanning power, scanning speed, and melt channel width, melt channel depth relationship matrix is established, wherein the melt channel width (melt width) and the melt channel depth (melt depth) are determined by measuring the width of the molten area and the depth of the overlapping weld of the top layer of the melt channel of the formed sample section through quantitative metallographic method, the required laser scanning power and scanning speed for realizing the keyhole melting mode and the corresponding melt channel width and depth are determined, and the table is as follows:

[0055]

[0056] (4) According to the relationship matrix between the laser scanning power, scanning speed, and melt channel width, melt channel depth obtained by the single-channel scanning test, under the condition that the melt channel depth is not less than 1.1 times the product of the powder laying thickness and the ratio of the theoretical density of the titanium alloy to the powder bulk density, the process parameter combination with a fast scanning speed is preferentially selected to determine that the laser scanning power is 260 W, the scanning speed is 1100 mm / s, the corresponding melt channel width is 214 μm, and the depth is 458 μm.

[0057] (5) After the laser scanning power and the scanning speed are determined, according to the melt channel width result of the single-channel scanning test, the scanning pitch is determined to be 107 μm according to 0.5 times the melt channel width.

[0058] (6) After the laser scanning of one layer is completed, the platform is lowered, and the lowering height is equal to the product of the set powder laying thickness and the ratio of the powder bulk density to the theoretical density of the titanium alloy, that is, 152.5 μm.

[0059] (7) The powder laying scraper lays the powder on the lowered powder bed on the platform.

[0060] (8) The laser scanning angle is counterclockwise rotated by 50°, and scanning is performed.

[0061] (9) Steps 7 and 8 are repeated until the forming of the part is completed, the powder bed is cleaned, and the dense part is obtained, and the forming efficiency is 101.7 cm 3 / hour, and after detection, the sample density is 99.9%.

Claims

1. A low cost high velocity selective laser melting titanium alloy forming method, characterized in that: The method comprises the following steps: (1) adjusting the laser to focus the laser beam spot diameter to 30-50 μm; (2) setting the powder laying thickness to 180-240 μm; (3) through multi-layer single-track scanning tests, a relationship matrix of laser scanning power, scanning speed and molten channel width and molten channel depth is established, the laser scanning power and scanning speed required for realizing the keyhole melting mode and the corresponding molten channel width and molten channel depth are determined, and a relationship matrix between the laser scanning power, scanning speed and molten channel width and molten channel depth is established; (4) according to the relationship matrix between the laser scanning power, scanning speed and molten channel width and molten channel depth obtained through the single-track scanning tests, the laser scanning power and scanning speed are determined according to the condition that the molten channel depth is not less than 1.1 times the product of the powder laying thickness and the ratio of the theoretical density of the titanium alloy to the powder bulk density; when a plurality of scanning power and scanning speed combinations can meet the molten channel depth requirement, the scanning speed is fast; (5) after the laser scanning power and scanning speed are determined, the scanning interval is determined according to the molten channel width result of the single-track scanning test, and the scanning interval is 0.4-0.5 times the molten channel width; (6) after the laser scanning of one layer is completed, the platform is lowered, and the lowering height is equal to the product of the set powder laying thickness and the ratio of the powder bulk density to the theoretical density of the titanium alloy; (7) the powder laying scraper lays the powder on the lowered powder bed on the platform; (8) the laser scanning angle is counterclockwise rotated by 33-66°, and scanning is performed; (9) steps 7 and 8 are repeated until the forming of the part is completed, the powder bed is cleaned, and a dense part is obtained.

2. The method of claim 1, wherein: In step (2), the powder used is titanium alloy spherical powder, and the maximum particle size is less than 60 μm.

3. The method of claim 1, wherein: In step (3), the number of layers in the multi-layer single-track test is 40, and the molten channel width and molten channel depth are determined by measuring the molten region width and the overlap welding depth of the top layer of the formed sample section through quantitative metallographic method.

4. The method of claim 1, wherein: A single laser is used, the wavelength of the laser is 1064 nm, and the power is not more than 500 W.

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