Powder bed fusion additive manufacturing method of unsupported overhanging structures and shaped parts

Abstract

The application relates to the field of SLM printing technology, aims to solve the problems of existing SLM technology forming overhanging surfaces needing to add supports or the poor surface quality of overhanging surfaces, and provides a support-free overhanging structure powder bed fusion additive manufacturing forming method and a formed part. The support-free overhanging structure powder bed fusion additive manufacturing forming method comprises the following steps: adopting pulse laser to perform laser scanning to sinter and form a first sintered thin layer; continuing to perform laser scanning by using pulse laser to sinter and form a second sintered thin layer on the first sintered thin layer; adopting continuous laser in a flat-top laser output mode to perform laser remelting scanning on the first sintered thin layer and the second sintered thin layer, and the energy of the continuous laser scanning meets the energy requirement of completely melting the second sintered thin layer and semi-melting the first sintered thin layer. The application has the beneficial effect that overhanging structures can be formed without supports, and the surface precision of the overhanging surface of the formed overhanging structure is high.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of SLM printing, in particular to a powder bed fusion additive manufacturing method for forming a support-free overhanging structure and a formed part. BACKGROUND

[0002] Laser powder bed fusion additive manufacturing, i.e., SLM (selective laser melting) printing technology, is an additive manufacturing technology that forms a printed part by melting and solidifying layer-by-layer laid metal powder through a laser.

[0003] Traditional laser powder bed fusion additive manufacturing has many problems when manufacturing parts with cavities and overhanging structures. On the one hand, printing with added support increases the time of printing the part, and on the other hand, it also increases the complexity of the post-processing process of the part. Reducing or eliminating support printing for laser powder bed fusion additive manufacturing is one of the difficult problems faced by the technology.

[0004] Some known technologies use a support-free printing method that uses a special laser scanning path to offset the scanning of the overhanging surface from the outside to the inside, balances the surface tension of the molten liquid when solidifying, and forms a sagging surface in rapid cooling to reduce the possibility of collapse of the overhanging surface, thereby omitting the addition of support structures. However, when the inclination angle of the overhanging surface relative to the printing plane is less than 45°, it is difficult to obtain an overhanging surface with high enough surface quality using this method.

[0005] Therefore, for the case where the inclination angle of the printing plane is less than 45°, it is generally necessary to add support structures in the industry, which greatly limits the application range of SLM technology. SUMMARY

[0006] The present application provides a powder bed fusion additive manufacturing method for forming a support-free overhanging structure and a formed part to solve the problem of the need for added support for forming an overhanging surface using existing SLM technology or poor surface quality of the overhanging surface.

[0007] In a first aspect, the present application provides a powder bed fusion additive manufacturing method for forming a support-free overhanging structure, comprising:

[0008] Step one: using a pulsed laser to perform laser scanning to sinter a first sintered thin layer, the first sintered thin layer being located at the first layer of the bottom surface of the overhanging structure;

[0009] Step two: continuing to use the pulsed laser to perform laser scanning to sinter a second sintered thin layer on the first sintered thin layer;

[0010] Step three: scanning the first sintered thin layer and the second sintered thin layer with a continuous laser in a flat-top laser output mode, the energy of the continuous laser scanning meeting the energy requirement of complete melting of the second sintered thin layer and semi-melting of the first sintered thin layer.

[0011] The powder bed fusion additive manufacturing method for forming a free-standing overhanging structure of the present application sintered the metal powder with a well-regulated pulsed laser to form a first sintered thin layer as the first layer of the bottom surface of the overhanging structure, and then continued to scan with a pulsed laser to form a second sintered thin layer on the basis of the first sintered thin layer. After forming the two layers of sintered thin layers, a flat-top continuous laser is used for remelting scanning. The continuous laser directly acts on the second sintered thin layer, and the second sintered thin layer can directly obtain the energy of the continuous laser, and obtains more energy; while the first sintered thin layer covered by the second sintered thin layer can only obtain part of the energy conducted by the second sintered thin layer, and obtains relatively less energy, therefore, the energy of the continuous laser can be regulated to melt the second sintered thin layer and semi-melt the first sintered thin layer. In addition, since the second sintered thin layer is sintered and formed, and the combination with the first sintered thin layer is not tight, no metallurgical combination is formed at the combination surface, and the heat conduction efficiency is relatively low, which is also conducive to achieving the purpose of melting the second sintered thin layer and semi-melting the first sintered thin layer without collapse by the continuous laser heating.

[0012] The first sintered thin layer has a relatively certain shape after sintering, and has small fluidity when heated by the continuous laser to be in a semi-melted state, and the deformation of the first sintered thin layer is small, so that the overhanging surface is not easy to collapse or have large deformation, and the surface precision of the first sintered thin layer as the first layer of the bottom surface of the overhanging structure is ensured, that is, the precision of the overhanging surface is ensured. Then, the second sintered thin layer has good fluidity after being heated and melted by the continuous laser, and can form a metallurgical combination with the first sintered thin layer heated to be in a semi-melted state at the combination surface, so as to ensure the combination between the layers to be dense, and achieve the structural performance reached by the ordinary SLM technology.

[0013] At the same time, since the continuous laser in the flat-top mode has uniform energy distribution, it can uniformly heat the sintered thin layer which has been sintered and solidified in the remelting process, avoiding the over-melting of the central region of the laser in the remelting process caused by the continuous laser in the Gaussian distribution, and avoiding the warping of the edge part to affect the powder laying of the subsequent layer.

[0014] Therefore, the powder bed fusion additive manufacturing method for forming a free-standing overhanging structure adopted by the present application can form an overhanging structure without support, and the surface precision of the bottom surface (overhanging surface) of the formed overhanging structure is high.

[0015] In a possible implementation, the layer thickness of the second sintered thin layer is less than the layer thickness of the first sintered thin layer.

[0016] In a possible implementation, the first sintered thin layer has a layer thickness of 30-45 μm, and the second sintered thin layer has a layer thickness of 15-25 μm.

[0017] In a possible implementation, the output pulse width of the pulsed laser is 1-1000 μm.

[0018] In a possible implementation, the output pulse width of the pulsed laser is 50-200 μm.

[0019] In a possible implementation, in the step three, the continuous laser heats the first sintered thin layer to 10-30 degrees Celsius above the melting point of the metal powder, so as to heat the first sintered thin layer to a semi-melted state with a liquid state ratio of 50-75%.

[0020] In a possible implementation, the inclination angle of the bottom surface of the overhanging structure is less than 45°. Further, the inclination angle of the bottom surface of the overhanging structure can be even lower than 10°.

[0021] In a possible implementation, the inclination angle of the bottom surface of the overhanging structure is less than 45°. Further, the inclination angle of the bottom surface of the overhanging structure can be even lower than 10°.

[0022] In a possible implementation, in the semi-melted state, the liquid state ratio of the metal powder is 50-75%.

[0023] In a possible implementation, the inclination angle of the bottom surface of the overhanging structure is less than 45°. Further, the inclination angle of the bottom surface of the overhanging structure can be even lower than 10°. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings in the embodiments will be briefly introduced as follows. It should be understood that the following drawings only show some of the embodiments of the present application, and therefore should not be considered as limiting the scope. For those skilled in the art, other related drawings can also be obtained without creative labor.

[0025] Figure 1 The model schematic diagram of the formed part of the embodiments of the present application;

[0026] Figure 2 The state diagram after step one is executed;

[0027] Figure 3 The state diagram after step two is executed;

[0028] Figure 4 State diagram for performing step three;

[0029] Figure 5 Schematic diagram for printing a shaped part.

[0030] Explanation of main component symbols:

[0031] Shaped part 10

[0032] Vertical portion 11

[0033] Horizontal portion 12

[0034] Overhanging face P1

[0035] First sintered thin layer 21

[0036] Second sintered thin layer 22

[0037] Bottom layer portion 23

[0038] Shaping cylinder 50

[0039] Metal powder 51 DETAILED DESCRIPTION

[0040] The technical solutions in the embodiments of the present application will be apparently and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments of the present application.

[0041] It should be noted that when an element is referred to as being "fixed" to another element, it can be directly on the other element or there can be an intervening element. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or there can be an intervening element. When an element is referred to as being "disposed" on another element, it can be directly on the other element or there can be an intervening element. The terms "vertical", "horizontal", "left", "right", and similar terms as used herein are for purposes of description only.

[0042] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0043] Some embodiments of the present application are described in detail. The following embodiments and features of the embodiments can be combined with each other in the case of no conflict.

[0044] Embodiment one

[0045] SLM printing technology is an additive manufacturing technology that forms a printed part by continuously melting and solidifying layer-by-layer deposited metal powder by laser. In a general SLM printing process, the metal powder is rapidly melted and solidified under laser heating to form a metallurgical bond, resulting in a dense and mechanically sound formed part.

[0046] Some formed parts have overhanging structures, for example Figure 1 The T-shaped formed part 10 shown includes a lower vertical portion 11 and an upper horizontal portion 12. The horizontal portion 12 is an overhanging structure, and its bottom surface (overhanging surface P1, which can be understood as an overhanging surface with an angle of less than 45° with the horizontal plane) extends beyond the vertical portion 11.

[0047] For formed parts with overhanging structures similar to Figure 1 If the conventional SLM forming method is directly used for forming, when the first layer of the bottom surface of the overhanging structure is printed and formed, the metal powder in this layer is melted by laser heating and has good fluidity, so it will flow and fill the gaps between the metal powder supported below under the action of gravity. After solidification, the surface of the lower surface (overhanging surface) of the structure will be uneven and have a large roughness.

[0048] The present embodiment provides a support-free overhanging structure powder bed fusion additive manufacturing forming method, which can form formed parts with overhanging structures similar to Figure 1 in a support-free manner and obtain an overhanging surface with good surface quality. The following will be specifically introduced with the formed part Figure 1 shown as an example.

[0049] The support-free overhanging structure powder bed fusion additive manufacturing forming method provided in the present embodiment uses a conventional continuous laser (such as a Gaussian laser) to perform layer-by-layer SLM laser scanning on the metal powder 51 in the forming cylinder 50, and after laser fusion forming of the vertical portion of the formed part is completed, the following steps are performed in sequence:

[0050] Step one: use pulsed laser to perform laser scanning to sinter a first sintered thin layer 21, which is located at the first layer of the bottom surface of the overhanging structure; see Figure 2 , the first sintered thin layer 21 is located on the layer above the formed vertical portion 11; the output pulse width of the pulsed laser used for sintering can be 1-1000 μm, and can be selected from 50-200 μm, such as 50 μm, 100 μm, 200 μm, etc.

[0051] Step two: continue to use the above-mentioned pulsed laser to perform laser scanning to sinter a second sintered thin layer 22 on the first sintered thin layer 21; see Figure 3 ;

[0052] Step three: using continuous laser with flat top laser output mode to scan and remelt the first sintered thin layer 21 and the second sintered thin layer 22, the energy of the continuous laser scanning meets the energy requirement of completely melting the second sintered thin layer 22 and semi-melting the first sintered thin layer 21, so that the first sintered thin layer 21 and the second sintered thin layer 22 are fused to form the bottom part 23 of the overhanging structure, see Figure 4 .

[0053] Subsequently, subsequent layer printing can be carried out according to the conventional SLM printing method to complete the printing of the horizontal part 12, so as to complete the printing of the entire overhanging structure (horizontal part) forming piece 10, see Figure 5 .

[0054] The support-free overhanging structure powder bed fusion additive manufacturing method of the embodiment forms the first sintered thin layer by the well-regulated pulsed laser, which is the first layer of the bottom surface of the overhanging structure, and then continues to form the second sintered thin layer by the pulsed laser scanning based on the first sintered thin layer. After forming the two layers of sintered thin layers, the remelt scanning is carried out by the flat-top continuous laser. It is proved in practice that the pulsed laser can more effectively control the melting-cooling solidification process of the scanning molten pool, and the metal powder is better formed and controlled by the heating mode of the pulsed laser, which is beneficial to achieve the expected effect of powder sintering or semi-melting. The continuous laser directly acts on the second sintered thin layer, and the second sintered thin layer can directly obtain the energy of the continuous laser, and the obtained energy is relatively more; while the first sintered thin layer covered by the second sintered thin layer can only obtain part of the energy conducted by the second sintered thin layer, and the obtained energy is relatively less, therefore, the energy of the continuous laser can be regulated to melt the second sintered thin layer and semi-melt the first sintered thin layer. In addition, because the second sintered thin layer is sintered and formed, and the combination with the first sintered thin layer is not tight, no metallurgical combination is formed at the combination surface, and therefore the heat conduction efficiency is relatively low, which is also beneficial to achieve the purpose of melting the second sintered thin layer and semi-melting the first sintered thin layer by the continuous laser heating without collapse.

[0055] The first sintered thin layer has a relatively certain shape after sintering, and has small fluidity when heated by the continuous laser to be in a semi-melted state, and the deformation of the first sintered thin layer is small, so that the overhanging surface is not easy to collapse or have large deformation, and the surface precision of the first sintered thin layer as the first layer of the bottom surface of the overhanging structure is ensured, i.e. the precision of the overhanging surface is ensured. Then, the second sintered thin layer has good fluidity after being heated and melted by the continuous laser, and can form a metallurgical combination with the first sintered thin layer heated to be in a semi-melted state at the combination surface, so as to ensure the compactness of the combination between the layers and achieve the structural performance reached by the conventional SLM technology.

[0056] Meanwhile, since the continuous laser with flat top mode has uniform energy distribution, the sintered solidified sintered thin layer can be uniformly heated during the remelting process, avoiding the collapse caused by excessive melting of the central region of the laser during the remelting process using the continuous laser with Gaussian distribution, or the warping of the edge portion affecting the powder laying of the subsequent layer.

[0057] Therefore, the powder bed fusion additive manufacturing forming method with support-free overhanging structure adopted in the embodiment can form an overhanging structure without support, and the surface precision of the bottom surface (overhanging surface) of the formed overhanging structure is high.

[0058] In the embodiment, the layer thickness of the second sintered thin layer is less than the layer thickness of the first sintered thin layer. Optionally, the layer thickness of the first sintered thin layer is 30-45 μm, and the layer thickness of the second sintered thin layer is 15-25 μm. For example, the layer thickness of the first sintered thin layer is 40 μm, and the layer thickness of the second sintered thin layer is 25 μm.

[0059] By setting the second sintered thin layer with smaller layer thickness and the first sintered thin layer with larger thickness, when the laser is remelted and scanned, the second sintered thin layer needs relatively less energy to achieve complete melting, while the first sintered thin layer has a larger layer thickness and is blocked by the second sintered thin layer, so it needs more energy of the continuous laser output to achieve complete melting, that is, the continuous laser has a larger output energy range to achieve the effect of complete melting of the second sintered thin layer and semi-melting of the first sintered thin layer.

[0060] In addition, the first sintered thin layer is set to be thicker, and it is also less likely to be excessively melted and collapsed during the continuous laser remelting, ensuring the surface precision of the bottom surface.

[0061] Optionally, in step three, the continuous laser heats the first sintered thin layer to 10-30 degrees Celsius above the melting point of the metal powder to heat the first sintered thin layer to a semi-melting state with a liquid fraction of 50-75%. Experimental results show that in the semi-melting state with a liquid fraction of 50-75%, the first sintered thin layer is less likely to collapse and can still maintain its shape precision, and can be fused together with the completely melted second sintered thin layer.

[0062] The powder bed fusion additive manufacturing forming method with support-free overhanging structure in the embodiment can be used to form other formed parts in addition to the formed part shown in the figure, which has a bottom surface of the overhanging structure with an inclination angle less than 45° and is set to be as low as 10° or below. Figure 1 The powder bed fusion additive manufacturing forming method with support-free overhanging structure in the embodiment can be used to form other formed parts in addition to the formed part shown in the figure, which has a bottom surface of the overhanging structure with an inclination angle less than 45° and is set to be as low as 10° or below.

[0063] Embodiment Two

[0064] The embodiment also provides a powder bed fusion additive manufacturing forming method of a free-standing overhanging structure, comprising: regulating pulse energy of a pulse laser to achieve input energy of semi-melting of metal powder for scanning printing, so as to obtain an overhanging surface of the overhanging structure, and a bottom layer thickness of the overhanging surface formed by the pulse laser is 20-60 μm. Optionally, in the semi-melting state, a liquid state proportion of the metal powder is 50-75%.

[0065] In this embodiment, the semi-melting state of the metal powder is obtained by directly scanning and heating by the pulse laser, and the semi-melting state of the metal powder with a liquid state proportion of 50-75% has more than half of the liquid state part, which is beneficial to fusion of each layer. Meanwhile, the semi-melting state of the metal powder has a solid state part, which ensures that the fluidity is smaller than that in the completely melting state, reduces the surface quality of the overhanging surface caused by excessive fluidity of the completely melting state, and thus the overhanging surface with better surface quality can be obtained.

[0066] The above embodiments are only used to illustrate the technical solutions of the present application but not limit the present application. Although the present application is described in detail with reference to the above preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the present application.

Claims

1. A free-standing overhanging structure powder bed fusion additive manufacturing forming method characterized by, The method comprises the following steps: step one, using a pulsed laser to perform laser scanning and sintering to form a first sintered thin layer on the bottom surface of the overhanging structure; step two, continuing to use the pulsed laser to perform laser scanning and sintering to form a second sintered thin layer on the first sintered thin layer; step three, using a continuous laser with a flat-top laser output mode to perform laser remelting scanning on the first sintered thin layer and the second sintered thin layer, the energy of the continuous laser scanning meets the energy requirement of complete melting of the second sintered thin layer and semi-melting of the first sintered thin layer; the layer thickness of the second sintered thin layer is less than that of the first sintered thin layer; the continuous laser heats the first sintered thin layer to 10-30 degrees Celsius above the melting point of the metal powder, so as to heat the first sintered thin layer to a semi-melting state with a liquid state ratio of 50-75%.

2. The unsupported overhanging structure powder bed fusion additive manufacturing forming method of claim 1 wherein, The layer thickness of the first sintered thin layer is 30-45 μm, and the layer thickness of the second sintered thin layer is 15-25 μm.

3. The free-standing overhanging structure powder bed fusion additive manufacturing forming method according to claim 1, wherein, The output pulse width of the pulsed laser is 1-1000 μm.

4. The unsupported overhanging structure powder bed fusion additive manufacturing forming method of claim 3, wherein, The output pulse width of the pulsed laser is 50-200 μm.

5. The unsupported overhanging structure powder bed fusion additive manufacturing forming method according to any one of claims 1-4, wherein, The inclination angle of the bottom surface of the overhanging structure is less than 45°.

6. A shaped part comprising an overhanging structure, characterized in that, The overhanging surface of the overhanging structure of the formed part is printed and formed by using the support-free overhanging structure powder bed fusion additive manufacturing forming method according to any one of claims 1-5.

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