Selective laser melting processing method and device

Abstract

The invention discloses a selective laser melting processing method and device, and relates to the technical field of laser additive manufacturing, and the selective laser melting processing method comprises the following steps: mixing raw materials according to a formula proportion, and grinding into powder with uniform particle size distribution; a powder raw material is added into a selective laser melting machining device, a first laser beam is applied to the surface of the raw material, and the first laser beam is large in light spot, low in energy density and used for preheating raw material powder; through the preheating and slow cooling effects of the first laser beam and the fourth laser beam, the temperature gradient is effectively reduced, the maximum stress is reduced, and cracking and peeling of a formed part are reduced; through melting of the second laser beam and the third laser beam, the porosity of a formed part is reduced through laser impact forging, and higher density and better mechanical performance and surface quality are obtained; the fourth laser beam further plays a role in in-situ heat treatment, residual heat generated by machining of the first three laser beams is fully utilized, and energy consumption is reduced; therefore, the performance and the forming quality of the formed part are improved through defect control and structure performance.

Description

Technical Field

[0001] The present invention relates to the technical field of laser additive manufacturing, and in particular to a selective laser melting processing method and device. Background Art

[0002] Selective laser melting is a major technical approach in additive manufacturing of metal materials. This technology uses laser as the energy source and scans the metal powder bed layer by layer according to the path planned in the 3D CAD slice model. The scanned metal powder is melted and solidified to achieve the metallurgical bonding effect, and finally the metal parts designed by the model are obtained.

[0003] At present, conventional processing methods use single laser for processing. During the processing, defects such as pores, cracks, spheroidization, spatter, poor surface quality and geometric deformation are prone to occur. Research has found that the main reasons are: pores are cavities formed by the failure of gas in the molten pool to escape in time during the solidification process; cracks are caused by the thermal stress of the material at high temperature; spheroidization is the spherical particles formed by metal powder during the solidification process, which affects the powder laying quality and the surface quality of the component, thereby reducing the tensile strength and fatigue resistance; geometric deformation is due to uneven temperature distribution. Residual stress will be generated in the cooling process of the parts, resulting in geometric deformation, affecting the dimensional accuracy and shape stability of the parts. Combined with the causes of defect formation, the present invention provides a selective laser melting processing method and device to solve the above problems. Summary of the invention

[0004] The object of the present invention is to provide a selective laser melting processing method and device to solve the problems existing in the prior art mentioned in the above background technology.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A selective laser melting method comprises the following steps:

[0007] S1: Mix the raw materials according to the formula ratio and grind them into powder with uniform particle size distribution;

[0008] S2: adding powder raw materials into the selective laser melting processing device, applying a laser beam 1 to the surface of the raw materials, wherein the laser beam 1 has a large spot and a low energy density, and is used for preheating the raw material powder;

[0009] S3: applying a second laser beam to the surface of the raw material, wherein the second laser beam has a small spot and a high energy density and is used to melt the preheated raw material powder;

[0010] S4: applying a third laser beam to the surface of the molten raw material, wherein the third laser beam is a pulsed laser with a small spot and a high energy density, and is used to perform laser impact forging on the molten layer;

[0011] S5: applying a laser beam four to the surface of the molded part. The laser beam four has a large spot and a relatively low energy density and is used for laser post-processing the molded part to complete the processing of the molded part.

[0012] Preferably, the power of the laser beam one is set to 150-250W, and the spot diameter is set to 140-160μm, the power of the laser beam two is set to 200-400W, and the spot diameter is set to 60-75μm; the power of the laser beam three is set to 230-450W, and the spot diameter is set to 60-75μm; the power of the laser beam four is set to 120-260W, and the spot diameter is set to 110-130μm.

[0013] Preferably, in S2, the powder raw material is evenly spread into a layered structure in a selective laser melting processing device using a powder spreading roller.

[0014] Preferably, the entire processing is carried out in a protective gas atmosphere.

[0015] Preferably, in S5, the cooling rate of the laser beam 24 is controlled by slow cooling after being applied to the molded part.

[0016] A selective laser melting processing device comprises a molding chamber, a molding cylinder and a material cylinder, wherein the molding cylinder and the material cylinder are respectively installed at both sides of the lower end of the molding chamber, an atmosphere protection system and a gas circulation purification system are installed at both ends of the molding chamber, and a powder spreading roller for evenly spreading powder raw materials is arranged inside the molding chamber;

[0017] A mirror frame is installed above the molding chamber, and a beam expander, a scanning galvanometer and an F-θ mirror are installed in the mirror frame in sequence. The mirror frame also includes a laser for emitting laser into the mirror frame. The laser is controlled by a computer control system, and the light beam emitted by the laser passes through the mirror frame and enters the molding chamber.

[0018] Preferably, the number of the lasers is four, three of which are continuous lasers and one is a pulsed laser.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention effectively reduces the temperature gradient, reduces the maximum stress, and reduces the cracking and peeling of the formed part through the preheating and slow cooling effects of the laser beam one and the laser beam four; reduces the porosity of the formed part through the melting and laser impact forging of the laser beam two and the laser beam three, and obtains a higher density, as well as better mechanical properties and surface quality; the laser beam four also plays an in-situ heat treatment role, fully utilizing the residual heat of the first three laser beams processing and reducing energy consumption; thereby improving the performance and forming quality of the formed part through defect control and organizational properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic structural diagram of the selective laser melting processing device of the present invention.

[0022] Figure 2 The SiC / Ti composite powder used in the examples and its size distribution diagram.

[0023] Figure 3 It is a comparison chart of XRD analysis results of the molding surface of conventional selective laser melting and this embodiment.

[0024] Figure 4 It is a comparison diagram of the surface morphology of conventional selective laser melting and the molding of this embodiment.

[0025] Figure 5 This is a comparison chart of the surface roughness of conventional selective laser melting and the molding of this embodiment.

[0026] Figure 6 This is a comparison of SEM photos of conventional selective laser melting and the molding of this embodiment.

[0027] Figure 7 This is a density comparison chart of the conventional selective laser melting and the molded parts of this embodiment.

[0028] Figure 8 This is a comparison chart of the microhardness of the parts formed by conventional selective laser melting and this embodiment.

[0029] Fig. 9 It is a comparison chart of the friction test results of the conventional selective laser melting and the molded parts of this embodiment.

[0030] Fig.10 It is a comparison diagram of the wear morphology of the molded parts by conventional selective laser melting and this embodiment.

[0031] Fig.11 It is a comparison chart of the tensile test results of the conventional selective laser melting and the molded part of this embodiment.

[0032] Fig.12 It is a comparison diagram of the tensile fracture morphology of the conventional selective laser melting and the molded part of this embodiment.

[0033] In the figure: 1. Molding chamber; 2. Molding cylinder; 3. Material cylinder; 4. Powder spreading roller; 5. Atmosphere protection system; 6. Gas circulation purification system; 7. Mirror frame; 8. Beam expander; 9. Scanning galvanometer; 10. F-θ mirror; 11. Laser; 12. Computer control system; 13. Light beam. DETAILED DESCRIPTION

[0034] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further explained below in conjunction with specific implementation methods.

[0035] See also Figure 1-12 , the present invention provides the following technical solutions:

[0036] A selective laser melting method comprises the following steps:

[0037] S1: Titanium powder (Ti) with an average particle size of 38.13 μm and 99.9% purity and silicon carbide particles (SiC) with an average particle size of 5 μm and 99.9% purity were used as raw materials; to ensure that the mixing ratio of the molded titanium powder and silicon carbide particles of the printed sample was 99:1, the mixed powder was ground by a planetary ball mill (Retsch PM100), and the grinding conditions were set as follows: a speed of 200 revolutions per minute, a ball-to-powder ratio of 5:1, and a grinding time of 3 hours. Figure 2 As shown in (a), the powder after grinding has a uniform particle size distribution, such as Figure 2 As shown in (b), the D50 value of the Ti / SiC mixed powder is 37.20 μm.

[0038] S2: Add powder raw materials into the selective laser melting processing device. The powder raw materials are evenly spread into a layered structure in the selective laser melting processing device by a powder spreading roller. A laser beam 1 is applied to the surface of the raw materials. The power of the laser beam 1 is set to 220W and the spot diameter is set to 150μm. The raw material powder is preheated to reduce the temperature gradient, reduce the maximum stress, and reduce the tendency of cracking and peeling of the formed parts.

[0039] S3: applying a second laser beam to the surface of the raw material, wherein the power of the second laser beam is set to 240 W and the spot diameter is set to 70 μm, to perform a melting process on the preheated raw material powder.

[0040] S4: Apply laser beam three to the surface of the molten raw material, wherein the power of the laser beam three is set to 280W and the spot diameter is set to 70μm, and the molten layer is laser impact forged. Its main function is to laser impact forge the molten layer, thereby reducing the porosity of the formed part, obtaining higher density and surface quality, and better mechanical properties.

[0041] S5: A laser beam four is then applied to the surface of the molded part. The power of the laser beam four is set to 200 W and the spot diameter is set to 120 μm. This is used for laser post-processing of the molded part to achieve slow cooling to reduce cracking and peeling of the molded part, in-situ heat treatment and tissue control. The entire processing process is carried out in a protective gas atmosphere. After the laser beam four is applied to the molded part, the cooling rate is controlled by slow cooling.

[0042] In the above process, the laser scanning speed is set to 1000mm / min, the scanning interval is set to 60μm, and the layer thickness is set to 30μm. In order to verify the superiority of the method of the present invention, the conventional selective laser melting technology is compared with the improved selective laser melting technology. The processed samples are characterized by different technical means, including X-ray diffraction (XRD), scanning electron microscopy (SEM), surface roughness, hardness, density, friction and wear performance, etc.

[0043] like Figure 3 As shown, the conventional selective laser melting sample and the improved processing sample were analyzed using X-ray diffraction (XRD) detection equipment, indicating that the original powders of the two processing methods are the same.

[0044] like Figure 4 As shown, the surface morphology of the conventional selective laser melting and the molded parts of this embodiment were observed by scanning electron microscopy (SEM). Figure 4 (a) The surface presents more pores, and this embodiment Figure 4 The surface of (b) is relatively smooth with almost no obvious pores. This improved method significantly improves the surface quality, reduces the formation of pores, and enhances the density of the material.

[0045] like Figure 5 As shown, the surface roughness of the conventional sample and the improved sample was measured by a surface roughness detection device. The surface roughness of the conventional sample was 19.3 μm, while the average surface roughness of this embodiment was 12.2 μm. The improved processing method significantly reduced the surface roughness and improved the surface smoothness.

[0046] like Figure 6 As shown in (a), the microstructure of the sample obtained by conventional selective laser melting is analyzed by SEM, and the sample exhibits a lamellar structure and larger particles, while Figure 6 As shown in (b), the improved sample presents a granular microscopic morphology, and the particle size is significantly reduced, which indicates that the processing method of this embodiment can effectively refine the material structure.

[0047] like Figure 7As shown, the density of the conventional selected area laser melting sample and the improved sample was analyzed by a density detector. The relative density of the conventional sample was 85%, while the relative density of this embodiment reached 95%, indicating that the improved processing method effectively improved the density of the sample.

[0048] like Figure 8 As shown, the hardness test results show that the average hardness of the conventional sample is 230HV, while the average hardness of the improved sample reaches 300HV. This shows that the processing method of this embodiment improves the hardness of the material, which is beneficial to enhancing its wear resistance.

[0049] like Fig. 9 As shown in the figure, the friction coefficient test shows that the friction coefficient of the conventional sample is 0.7, while the friction coefficient of this embodiment is 0.6, showing better friction reduction performance. Fig.10 As shown in (a), SEM analysis of the wear morphology shows that the conventional sample mainly exhibits abrasive wear, while Fig.10 As shown in (b), the improved sample exhibits adhesive wear, indicating that the improved processing method can improve the friction and wear performance.

[0050] like Fig.11 As shown in FIG. 1 , the tensile test results show that the average tensile strength of the conventional selective laser melting sample is 950 MPa, while the tensile strength of the sample in this embodiment is 1100 MPa. Fig.12 As shown in (a), the SEM analysis of the tensile fracture morphology shows that the conventional sample has more pores on the fracture surface, while the Fig.12 The fracture surface quality of the sample (b) is better and there are fewer pores, indicating that the fracture toughness and tensile properties of the material have been significantly improved.

[0051] It can be seen from the experimental results of the implementation cases of the present invention that the improved selective laser melting processing method significantly improves the density, hardness, friction performance and tensile strength of the material compared with the conventional selective laser melting method. The composite material processed by this method has better surface quality and microstructure, and is suitable for the manufacture of high-performance materials. This technology can effectively improve the application performance of composite materials under high load and high wear environments, and has broad application prospects.

[0052] The present invention also provides a selective laser melting processing device, comprising a molding chamber 1, a molding cylinder 2 and a material cylinder 3, wherein the molding cylinder 2 and the material cylinder 3 are respectively installed at both sides of the lower end of the molding chamber 1, and an atmosphere protection system 5 and a gas circulation purification system 6 are installed at both ends of the molding chamber 1, wherein the gas circulation purification system 6 is used to clean the residual dust and gas in the processing environment; the atmosphere protection system 5 is used to provide a protective atmosphere during the processing. A powder laying roller 4 for evenly laying the powder raw material is provided inside the molding chamber 1, and the powder laying roller 4 is used to evenly lay the powder layer; the material cylinder 3 and the molding cylinder 2 are used to store and support the processing material.

[0053] A mirror frame 7 is installed above the molding chamber 1, and a beam expander 8, a scanning galvanometer 9 and an F-θ mirror 10 are installed in the mirror frame 7 in sequence, and also includes a laser 11 for emitting laser into the mirror frame 7. The number of the lasers 11 is provided with four sets, of which three sets are continuous lasers and one set is a pulse laser. The pulse width and repetition frequency of the pulse laser can be adjusted according to the material characteristics of the molded part; the laser 11 is controlled by a computer control system 12, and the light beam 13 emitted by the laser 11 enters the molding chamber 1 after passing through the mirror frame 7; the laser system can realize the functions of preheating, melting, impact and heat treatment respectively.

[0054] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A selective laser melting method, characterized in that: The following steps are involved: S1: Mix the raw materials according to the formula ratio and grind them into powder with uniform particle size distribution; S2: adding powder raw materials into the selective laser melting processing device, applying a laser beam 1 to the surface of the raw materials, wherein the laser beam 1 has a large spot and a low energy density, and is used for preheating the raw material powder; S3: applying a second laser beam to the surface of the raw material, wherein the second laser beam has a small spot and a high energy density and is used to melt the preheated raw material powder; S4: applying a third laser beam to the surface of the molten raw material, wherein the third laser beam is a pulsed laser with a small spot and a high energy density, and is used to perform laser impact forging on the molten layer; S5: applying a laser beam four to the surface of the molded part. The laser beam four has a large spot and a relatively low energy density and is used for laser post-processing the molded part to complete the processing of the molded part.

2. The selective laser melting method according to claim 1, characterized in that: The power of the laser beam one is set to 150-250W, and the spot diameter is set to 140-160μm, the power of the laser beam two is set to 200-400W, and the spot diameter is set to 60-75μm; the power of the laser beam three is set to 230-450W, and the spot diameter is set to 60-75μm; the power of the laser beam four is set to 120-260W, and the spot diameter is set to 110-130μm.

3. The selective laser melting method according to claim 1, characterized in that: In S2, the powder raw material is evenly spread into a layered structure in a selective laser melting processing device using a powder spreading roller.

4. The selective laser melting method according to claim 1, characterized in that: The entire processing is carried out in a protective gas atmosphere.

5. The selective laser melting method according to claim 1, characterized in that: In S5, after the laser beam 24 is applied to the molded part, the cooling rate is controlled by slow cooling.

6. A selective laser melting processing device used in the processing method according to any one of claims 1 to 5, characterized in that: The invention comprises a molding chamber (1), a molding cylinder (2) and a material cylinder (3), wherein the molding cylinder (2) and the material cylinder (3) are respectively installed at both sides of the lower end of the molding chamber (1), an atmosphere protection system (5) and a gas circulation purification system (6) are installed at both ends of the molding chamber (1), and a powder spreading roller (4) for evenly spreading powder raw materials is provided inside the molding chamber (1); A mirror frame (7) is installed above the molding chamber (1), and a beam expander (8), a scanning galvanometer (9) and an F-θ mirror (10) are installed in sequence in the mirror frame (7), and also includes a laser (11) for emitting laser light into the mirror frame (7). The laser (11) is controlled by a computer control system (12), and a light beam (13) emitted by the laser (11) passes through the mirror frame (7) and enters the molding chamber (1).

7. The selective laser melting processing device according to claim 6, characterized in that: The number of the lasers (11) is four, three of which are continuous lasers and one is a pulse laser.

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