A supported laser selective melting additive manufacturing method

Abstract

The application discloses a kind of unsupported laser selective melting additive manufacturing methods, it is related to additive manufacturing technical field, including the following steps: S1, layer-by-layer powder laying, printing in entity support area;S2, for the powder layer containing overhanging surface, process overhanging area, while processing entity support area;Including the following steps: S21, process single-layer overhanging surface;S22, remelt, make the overhanging layer obtained in step S21 form stable continuous molten pool when laser scanning, and solidify stably, form continuous single layer;S23, process entity support area;S3, forming cylinder is lowered one layer thickness, powder laying;S4, repeat step S2-S3, until overhanging structure has preset thickness;S5, continue layer-by-layer powder laying, printing in entity support area and overhanging structure foundation.The application can realize small-angle even horizontal surface unsupported printing, increase design freedom, reduce processing time and workload, reduce post-processing cost.

Description

Technical Field

[0001] This invention relates to the field of additive manufacturing technology, and in particular to a supportless laser selective melting additive manufacturing method. Background Technology

[0002] Additive manufacturing (AM), commonly known as 3D printing, is a technology that manufactures parts by layering materials, unlike traditional machining techniques. It has broad application prospects in aerospace, automotive, biomedical, and industrial production.

[0003] Selective Laser Melting (SLM) / Laser Powder Bed Laser Fusion (LPBF) is a commonly used additive manufacturing technology. Its principle is as follows: a 3D CAD model of the part is divided into two-dimensional planes of predetermined thickness. Powder is laid flat on a substrate, and a laser selectively melts corresponding areas on the powder bed, forming a dense cross-section of the part. After one layer is processed, the forming cylinder is lowered by one layer thickness, and another layer of powder is laid on top and scanned by the laser. This process of laying powder layer by layer and processing the two-dimensional cross-section layer by layer is continued until the 3D part is completed. Theoretically, any complex spatial geometry can be transformed into cross-sectional information that can be scanned layer by layer by the laser after slicing. Therefore, SLM technology is theoretically almost unrestricted by the complexity of the part, enabling high-precision and rapid processing of complex parts.

[0004] However, in the SLM / LPBF process, complex shapes often result in overhanging / tilted lower surfaces. This means that the sides / tilted / overhanging lower surfaces of the part are not supported by the previously formed solid part, but are partially / directly exposed to the underlying powder. Because this surface lacks solid support, the molten pool formed during laser melting tends to agglomerate into droplets (spheroidization) due to surface tension. Furthermore, since the heat transfer capacity of powder particles is much lower than that of a continuous solid, this affects the heat dissipation and cooling of the molten pool, leading to processing failure. In actual printing, for lower surfaces with outward tilt angles exceeding a certain threshold (generally 45°), a support structure needs to be added outside the part design to make the molten pool more stable and enhance local heat dissipation.

[0005] However, setting up support structures increases the volume / workload required for printing, increases printing time, material costs, and post-processing costs for removing support structures, and the quality of the lower surface is often relatively rough. In addition, for shapes that are difficult to machine with traditional cutting methods, such as internal channels and cavities, it is also difficult to remove the support structures at the corresponding locations, and the surface quality of the corresponding parts is also difficult to improve effectively through post-processing. This problem also limits the application scope of 3D printing. Summary of the Invention

[0006] The purpose of this invention is to provide a supportless laser selective melting additive manufacturing method to solve the above-mentioned problems existing in the prior art. It can realize supportless printing at small angles or even on horizontal planes, increase design freedom, reduce processing time and workload, reduce post-processing costs, and realize supportless direct forming of complex shapes.

[0007] To achieve the above objectives, the present invention provides the following solution:

[0008] This invention provides a supportless laser selective melting additive manufacturing method, comprising the following steps:

[0009] S1. Apply powder layer by layer and print in the solid support area;

[0010] S2. In the powder layer containing the overhanging surface, process the overhanging structure, and simultaneously process the solid support area; specifically including the following steps:

[0011] S21. Process a single-layer overhanging surface, control the laser energy input, and make the laser scan the powder in the overhanging area and adjacent areas with low energy density to achieve heating or local melting of the powder surface irradiated by the laser. Control the laser energy input to keep the particles in the powder layer in their original positions, so that they neither evaporate significantly nor completely melt to form a continuous molten pool, thereby achieving melting or sintering of the powder particle surface in the scanning area, establishing a connection between the powder particles, and forming a loose overhanging layer; wherein, the overhanging layer completely covers the cross section of the part to be printed;

[0012] S22. Remelting: The part area included in step S21 is re-scanned with a laser, so that the overhanging layer in step S21 melts after the laser scan to form a stable and continuous molten pool, and then solidifies stably to form a continuous part cross-section sheet.

[0013] S23. Process the remaining solid support area of ​​the current layer, and connect the overhanging structure with the adjacent solid support area to form the cross section of the single-layer part to be processed.

[0014] S3. The forming cylinder descends by one layer thickness to spread powder;

[0015] S4. Repeat steps S2 to S3 until the overhanging structure has a preset thickness;

[0016] S5. On the basis of the solid support area and the hanging structure, powder is applied layer by layer and printed to process the solid support area and the hanging structure simultaneously until the part is printed and taken out for post-processing.

[0017] Preferably, in step S21, one, two, or three of the following methods are used to control the laser energy input: reducing laser power, increasing scanning speed, and / or expanding the laser spot.

[0018] Preferably, in step S21, the overhang layer covers only the cross-section of the part to be printed, or covers an area enlarged based on the cross-section of the part.

[0019] Preferably, in step S22, by controlling the energy density, scanning speed, scanning line spacing and interval time, the sintered layer in step S21 melts after laser scanning to form a stable continuous molten pool, and then solidifies stably to form a continuous sheet.

[0020] Preferably, in step S4, steps S2 to S3 are repeated 1 to 20 times until the thickness of the overhang structure can provide stable solid support for subsequent powder scanning.

[0021] Preferably, after step S5, the method further includes the following step:

[0022] S6. Continue printing the part, remove the powder from the molding chamber, and remove the part from the substrate for post-processing.

[0023] The present invention achieves the following beneficial technical effects compared to the prior art:

[0024] In this invention, powder is pre-laid in the overhanging area. During the processing of the overhanging structure, the powder surface is first melted or sintered using a laser. Without disturbing the original position of the powder, connections are first established between the powder particles to form a relatively loose overhanging layer. Then, remelting is performed to improve the connection quality and density, forming a continuous single-layer part cross-section sheet. The above process is repeated until the overhanging structure has a certain thickness, forming a near-solid structure, which can then be processed using conventional methods. This invention enables supportless printing at small angles or even on horizontal planes, increasing design freedom, reducing processing time and workload, reducing post-processing costs, and achieving direct forming without relying on support structures. At the same time, it can also improve the surface quality of the overhanging structure and enhance product performance. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of unsupported laser selective melting additive manufacturing in an embodiment of the present invention;

[0027] Figure 2 This is a schematic diagram of the layer-by-layer machining of parts in an embodiment of the present invention.

[0028] In the diagram: 1-substrate, 2-inclined suspension structure, 3-horizontal suspension structure, 4-solid support area. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] The purpose of this invention is to provide a supportless laser selective melting additive manufacturing method to solve the above-mentioned problems existing in the prior art. It can realize supportless printing at small angles or even on horizontal planes, increase design freedom, reduce processing time and workload, reduce post-processing costs, and realize supportless direct forming of complex shapes.

[0031] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0032] Example 1

[0033] like Figure 1 and Figure 2 As shown, this embodiment provides a supportless laser selective melting additive manufacturing method, which mainly includes the following steps:

[0034] S1. The solid support area 4 of the part is processed using existing common processing methods, that is, powder is laid and printed layer by layer in the solid support area 4. Printing is laser scanning and melting of powder material, which is a mature existing technology in this field and will not be described in detail in this embodiment. Moreover, it should be noted that during the process of powder laying and printing layer by layer in the solid support area 4, powder is also laid in the overhang area until the powder laying height in the overhang area reaches the bottom height of the overhang structure to be processed.

[0035] Furthermore, it should be noted that in this embodiment, the solid support area 4 refers to the area processed layer by layer from bottom to top on the substrate 1, while the overhang area is the area with a gap between it and the substrate 1. The overhang area can be processed with inclined overhang structure 2 and horizontal overhang structure 3.

[0036] S2. In the powder layer containing the overhanging surface, process the overhanging structure, and simultaneously process the solid support area 4; specifically including the following steps:

[0037] S21. Process a single-layer overhanging surface, control the laser energy input, and use a laser to scan the powder in the overhanging area and adjacent areas at a low energy density. Specifically, by reducing the laser power, increasing the scanning speed, and expanding the laser spot, the overhanging area and its adjacent areas (i.e., the area adjacent to the overhanging area on the solid support area 4 of the same part slice) are scanned to achieve heating or local melting of the powder surface irradiated by the laser. The laser energy input is controlled to keep the powder layer basically in its original position after irradiation, without significant evaporation or the formation of a continuous molten pool, so as to achieve melting or sintering of the powder particle surface, establish connections between the powder particles, and form a relatively loose overhanging layer. The overhanging layer completely covers the cross-section of the part to be printed. Specifically, depending on the different powder materials and local part characteristics, the processing area in this step needs to cover the cross-section of the part to be printed. It can be either covering only the cross-section area of ​​the part to be printed, or covering the area enlarged according to the cross-section of the part. The extra part of the processing area is relatively loose and can be removed after printing.

[0038] Among them, low energy density refers to a lower energy density relative to the processing entity support area 4. The specific energy density can be set according to specific work needs.

[0039] S22. Remelting: The part area included in step S21 is re-scanned using a laser. The energy density, scanning speed, scanning line spacing and interval time are controlled so that the overhang layer in step S21 melts after the laser scan to form a stable continuous molten pool and solidifies stably to form a continuous part cross-sectional sheet. The part cross-sectional sheet located in the overhang area is a single-layer overhang structure. Multiple overhang structure layers constitute a complete overhang structure.

[0040] S23. Process the remaining solid support area 4 of the current layer, and connect the overhang structure with the adjacent solid support area 4 to form the cross section of the single-layer part to be processed.

[0041] S3. The forming cylinder descends by one layer thickness to spread powder;

[0042] S4. Repeat steps S2 to S3 until the overhanging structure has a preset thickness, which can provide stable solid support for subsequent powder scanning; wherein, when repeating step S2, i.e. sintering and then remelting, the new layer of powder material first establishes surface connections (meaning without damaging the particle positions of the powder layer; if the surface temperature is too high, molten droplets will form, and when the evaporation temperature is reached, powder particles will splatter), and then remelts to form a dense single layer. The melting depth of the remelting process must reach the position of the lower layer to achieve stable connection, while controlling the volume and depth of the molten pool to ensure that the previous structure is not damaged;

[0043] S5. Process the overhanging area and the solid support area 4 using a process similar to or the same as that used for conventional parts. That is, continue to apply powder and print layer by layer on the solid support area 4 and the overhanging structure according to the normal printing process, so as to process the solid support area 4 and the overhanging area simultaneously until the part is printed and taken out for post-processing.

[0044] In this embodiment, in step S4, steps S2 to S3 are repeated 1-20 times until the thickness of the overhang structure can provide stable solid support for subsequent powder scanning.

[0045] In this embodiment, after step S5, the following step is further included:

[0046] S6. Continue printing the part, remove the powder from the molding chamber, and remove the part from the substrate 1.

[0047] In this invention, powder is pre-laid in the overhanging area. When processing the overhanging structure, the powder surface is first melted or sintered using a laser. Without disturbing the original position of the powder, connections are first established between the powder particles to form a relatively loose overhanging layer. Then, remelting is performed to improve the connection quality and density, forming a dense single-layer part cross-section sheet. The above process is repeated until the overhanging structure has a certain thickness, forming a near-solid structure, which can then be processed using conventional methods. This invention enables supportless printing at small angles or even on horizontal planes, increasing design freedom, reducing processing time and workload, reducing post-processing costs, and achieving direct forming without relying on support structures. At the same time, it can also improve the surface quality of the overhanging structure and enhance product performance.

[0048] It should be noted that, for those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention, and no reference numerals in the claims should be construed as limiting the scope of the claims.

[0049] Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. Furthermore, those skilled in the art will recognize that, based on the ideas of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A supportless laser selective melting additive manufacturing method, characterized in that: Includes the following steps: S1. Apply powder layer by layer and print in the solid support area; S2. In the powder layer containing the overhanging surface, process the overhanging structure, and simultaneously process the solid support area; specifically including the following steps: S21. Process a single-layer overhanging surface, control the laser energy input, and make the laser scan the powder in the overhanging area and adjacent area with low energy density to achieve heating or local melting of the powder surface irradiated by the laser. Control the laser energy input to keep the particles in the powder layer in their original positions, so that they neither evaporate significantly nor completely melt to form a continuous molten pool, thereby achieving melting or sintering of the powder particle surface in the scanning area, establishing a connection between the powder particles, and forming a loose overhanging layer; wherein, the adjacent area is the area on the solid support area of ​​the same part slice that is adjacent to the overhanging area, and the overhanging layer covers the area enlarged according to the cross-section of the part; S22. Remelting: The part area included in step S21 is re-scanned with a laser, so that the overhanging layer in step S21 melts after the laser scan to form a stable and continuous molten pool, and then solidifies stably to form a continuous part cross-section sheet. S23. Process the remaining solid support area of ​​the current layer, and connect the overhang structure with the adjacent solid support area to form the cross section of the single-layer part to be processed. S3. The forming cylinder descends by one layer thickness to spread powder; S4. Repeat steps S2 to S3 until the overhanging structure has a preset thickness. When repeating step S2, sintering is performed first and then remelting is performed to establish a surface connection of the new layer of powder material and then remelt it to form a dense single layer. The melting depth of the remelting process should reach the position of the lower layer to achieve a stable connection. At the same time, the volume and depth of the molten pool are controlled to ensure that the previous structure is not damaged. S5. On the basis of the solid support area and the hanging structure, powder is applied layer by layer and printed to process the solid support area and the hanging structure simultaneously until the part is printed and taken out for post-processing.

2. The unsupported laser selective melting additive manufacturing method according to claim 1, characterized in that: In step S21, the laser energy input is controlled by any one, two or three of the following methods: reducing laser power, increasing scanning speed, and expanding laser spot size.

3. The unsupported laser selective melting additive manufacturing method according to any one of claims 1-2, characterized in that: In step S22, by controlling the energy density, scanning speed, scanning line spacing and interval time, the sintered layer in step S21 melts after laser scanning to form a stable continuous molten pool, and then solidifies stably to form a continuous sheet.

4. The unsupported laser selective melting additive manufacturing method according to claim 1, characterized in that: In step S4, steps S2 to S3 are repeated 1-20 times until the thickness of the overhang structure can provide stable solid support for subsequent powder scanning.

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