Powder laying type multi-laser additive and subtractive composite manufacturing method

Abstract

The invention discloses a powder laying type multi-laser additive and subtractive composite manufacturing method. The method comprises the steps that a part shape outline is melted on powder through forming laser; performing in-situ scanning on the shape contour of the part by using ultrafast laser; according to the pre-tested material reduction thickness h, the substrate is controlled to be integrally lifted by h, and the position, not cut, of the part shape is lifted to the effective focal length range of ultrafast laser; after the current layer is scanned for one or more times through the ultrafast laser, the lifting mechanism at the bottom of the forming bin drives the base plate to integrally rise for h again, the ultrafast laser is used again for conducting material reduction on the shape contour of the part, execution is repeated till the total rising height ht of the base plate is larger than the material increase height H, and then material reduction is finished; and a lifting mechanism at the bottom of the forming bin drives the base plate to be lowered by hn + H, the powder scraper paves the metal powder with the thickness being H on the base plate, and the material adding process of the next layer is conducted till the whole part printing process is finished. The purpose of multi-laser additive and subtractive composite manufacturing with the compensation height is achieved.

Description

Technical Field

[0001] The present invention relates to a 3D printing method, and particularly to a powder spreading type multi-laser additive and subtractive manufacturing method. Background Art

[0002] Selective Laser Melting (SLM), as a common process for metal additive manufacturing, can achieve near-net shaping of complex-structured parts by layer-by-layer melting of a metal powder layer with an infrared laser (usually with a wavelength of 1064 nm).

[0003] Compared with traditional machining, one shortcoming in the metal additive manufacturing process is that the surface roughness of the part is relatively high. Due to the layer-by-layer printing feature of the additive process, step effects will appear at the edges between layers. Especially when printing an inclined surface, a phenomenon similar to the stepped surface of a pyramid will unavoidably appear on the surface. This makes it necessary to remove these steps by methods such as grinding after the part is printed, so as to make the surface roughness of the part meet the usage requirements.

[0004] However, for parts with complex internal cavity structures, after printing, due to the large and complex internal cavities, it is very difficult to insert a grinding tool from the outside, so it is very difficult to grind or polish the internal structure, and methods such as abrasive flow are not applicable either. Currently, most additive and subtractive solutions adopt a solution that combines Laser Engineered Net Shaping (DED) with a machining center to achieve subtraction while adding material during the additive process. However, this method has shortcomings such as a complex control algorithm. In addition, in a multi-laser additive and subtractive solution, since the effective focal depths of the forming laser used for additive manufacturing and the ultrafast laser used for subtractive manufacturing are not the same, a phenomenon that the single layer thickness of the additive material cannot be completely cut through by the subtractive process easily occurs. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a multi-laser additive and subtractive manufacturing method with compensated height for problems such as inconsistent effective focal lengths of different types of lasers during the multi-laser additive and subtractive forming process in the prior art.

[0006] To solve the above technical problem, the present invention adopts the following technical solutions.

[0007] A powder spreading type multi-laser additive and subtractive manufacturing method, which comprises the following steps: Step S1, using a powder doctor blade of a metal selective laser melting printing device to spread metal powder with a thickness of H on a substrate; Step S2, using a forming laser to melt out the part shape contour on the powder; Step S3, using an ultrafast laser to perform in-situ scanning on the part shape contour; Step S4, according to the pre-tested subtractive thickness h, controlling the lifting mechanism at the bottom of the forming chamber of the metal selective laser melting printing device to drive the substrate to rise as a whole by h, and raising the position where the part shape in Step S3 is not cut to within the effective focal length range of the ultrafast laser; Step S5, after using the ultrafast laser to scan the current layer once or multiple times, the lifting mechanism at the bottom of the forming chamber drives the substrate to rise as a whole by h again, and uses the ultrafast laser to perform subtractive processing on the part shape contour again. Repeat Step S5 until the total height h t of the substrate rises is greater than the additive height H, and then the subtractive processing ends, where h t = h n *n, n is the number of rises; Step S6, the lifting mechanism at the bottom of the forming chamber drives the substrate to lower the height h n + H, the powder doctor blade spreads metal powder with a thickness of H on the substrate, and performs the additive process of the next layer; Repeat Steps S1 to S6 until the entire part printing process ends.

[0008] Preferably, in Step S1, the metal selective laser melting printing device includes an inert gas protected printing space, and the substrate is located in the inert gas protected printing space.

[0009] Preferably, in Step S1, the metal powder can be a non-metal powder or a multi-metal mixed powder.

[0010] Preferably, in Step S2, the part shape contour includes an inner contour and an outer contour of the part.

[0011] Preferably, in Step S1, the powder spreading thickness H is 20 microns to 180 microns.

[0012] Preferably, the ultrafast laser is a femtosecond or picosecond laser.

[0013] In the powder spreading type multi-laser additive and subtractive manufacturing method disclosed by the present invention, in an inert gas protected printing space, a powder spreading device evenly spreads powder on a substrate. After the metal powder forms a thin layer, one or more forming laser optical modules focus the light beam according to a preset trajectory, instantaneously heating the powder above the melting point. After completing the single-layer sintering, the substrate descends by a layer thickness, and the cycle of powder spreading, scanning, and melting is repeated, layer by layer stacking until the printing of the entity is completed. When the above printing program is set, the printing layer thickness is H, and the total height of the part is H t=H*n, where the printing thickness H is the powder spreading layer thickness during printing. In the above multi-laser additive and subtractive manufacturing process, the additive process is the same as the principle of traditional SLM. The difference is that after each layer of printing is completed, one or more ultrafast laser optical modules are enabled to scan the edge of the printed shape to achieve subtractive processing, aiming to reduce the staircase effect between layers, thereby reducing the surface roughness of the part. At the same time, it solves the problem that the effective focal lengths of different types of lasers are inconsistent in the multi-laser additive and subtractive forming process in the prior art, achieving the purpose of multi-laser additive and subtractive composite manufacturing with height compensation. Description of the Drawings

[0014] Figure 1 It is a schematic structural diagram of a metal selective laser melting printing device; Figure 2 It is a schematic diagram of the part layer structure during the forming laser printing process; Figure 3 It is a schematic diagram of the part scanning position after the ultrafast laser scans once; Figure 4 It is a schematic diagram of the part scanning position after the ultrafast laser scans again; Figure 5 It is a schematic diagram of the part scanning position after the ultrafast laser scans n times; Figure 6 It is a flow chart of the ultrafast laser multiple scanning process; Figure 7 It is a flow chart of the powder spreading multi-laser additive and subtractive composite manufacturing method of the present invention. Detailed Embodiments

[0015] The present invention will be described in more detail below with reference to the drawings and embodiments.

[0016] Refer to Figure 3 , define H therein as the single-layer printing thickness of the forming laser, and h as the effective removal height of the ultrafast laser; Refer to Figure 4 , h1 is the effective removal height of the ultrafast laser after each layer of additive manufacturing is completed; Refer to Figure 5 , indicating that the lifting platform finally moves up by h n , enabling the ultrafast laser to complete the subtractive processing of this layer; Refer to Figure 6 , showing the scanning process, and successively showing the states of three stages from left to right: In the first figure, after each layer of additive manufacturing is completed, the effective removal height h1 of the ultrafast laser is used; In the second figure, then the lifting platform moves up by h1 so that the ultrafast laser can continue to effectively remove the surface downward; In the third figure, the lifting platform finally moves up by h n, enabling the ultrafast laser to complete the subtractive process of this printing layer, and then the lifting platform descends to a height of h n +H for additive printing of the next layer.

[0017] The present invention discloses a powder spreading type multi-laser additive and subtractive composite manufacturing method, which combines Figures 1 to 7 As shown, it includes the following steps: Step S1, using the powder doctor blade of the metal selective laser melting printing equipment to spread metal powder with a thickness of H on the substrate; Step S2, using the shaping laser to melt out the part shape contour on the powder; Step S3, using the ultrafast laser to perform in-situ scanning on the part shape contour; Step S4, according to the pre-tested subtractive thickness h, controlling the lifting mechanism at the bottom of the forming chamber of the metal selective laser melting printing equipment to drive the substrate to rise as a whole by h, and raising the position where the part shape in step S3 is not cut to within the effective focal length range of the ultrafast laser; Step S5, after scanning the current layer one or more times with the ultrafast laser, the lifting mechanism at the bottom of the forming chamber drives the substrate to rise as a whole by h again, and uses the ultrafast laser to perform subtraction on the part shape contour again. Repeat step S5 until the total height h t risen by the substrate is greater than the additive height H, and then the subtraction ends, where h t =h n *n, where n is the number of rises; Step S6, the lifting mechanism at the bottom of the forming chamber drives the substrate to lower by a height of h n +H, and the powder doctor blade spreads metal powder with a thickness of H on the substrate to perform the additive process of the next layer; Repeat steps S1 to S6 until the entire part printing process ends.

[0018] In the above method, in an inert gas protected printing space, the powder spreading device evenly spreads the powder on the substrate. After the metal powder forms a thin layer, one or more shaping laser optical modules focus the beam according to a preset trajectory, instantaneously heating the powder above the melting point. After completing the single-layer sintering, the substrate descends by one layer thickness, repeating the cycle of powder spreading, scanning, and melting, layer by layer stacking until the printing of the entity is completed. When setting the above printing program, the printing layer thickness is H, and the total height of the part is H t=H*n, where n = 1, 2, 3, 4..., and the printing thickness H is the powder spreading layer thickness during printing. In the above multi-laser additive and subtractive manufacturing process, the additive process is the same as the traditional SLM principle. The difference is that after each layer of printing is completed, one or more ultrafast laser optical modules are enabled to scan the edge of the printed shape to achieve subtractive processing. The purpose is to reduce the staircase effect between layers, thereby reducing the surface roughness of the part. At the same time, it solves the problems in the prior art such as inconsistent effective focal lengths of different types of lasers in the multi-laser additive and subtractive forming process, achieving the purpose of multi-laser additive and subtractive composite manufacturing with height compensation.

[0019] Since the structures of the parts prepared by additive and subtractive manufacturing are generally relatively complex, for the convenience of explaining the technical principle of the present invention, a rectangle is used to represent the printing layer as an example for explanation.

[0020] In this embodiment, after the multi-lasers and supporting optical modules such as galvanometers and field lenses are installed on the additive and subtractive manufacturing equipment, since the melting depth of the forming laser is sometimes greater than the subtractive thickness of the ultrafast laser, directly performing in-situ subtraction cannot completely cut through the printing layer, that is, it is difficult to effectively reduce the surface roughness of the inner and outer surfaces of the part.

[0021] During actual processing, generally, the parameters of the ultrafast laser need to be tested to find the optimal subtractive thickness h, and here it is assumed that the powder spreading thickness set in the additive process is H.

[0022] As the core step of this embodiment, when the additive thickness H is greater than the subtractive thickness h, one or more layers can be printed first, and then the lifting mechanism at the bottom of the forming chamber is gradually raised layer by layer according to the subtractive height h to achieve layer-by-layer subtraction of the printed contour. After the subtraction is completed, the forming chamber substrate is lowered back to the additive position.

[0023] In step S1 of this embodiment, the metal selective laser melting printing equipment includes an inert gas protected printing space, and the substrate is located in the inert gas protected printing space. Further, in step S1, the metal powder can be a non-metal powder or a multi-metal mixed powder.

[0024] As a preferred method, in step S2, the part shape contour includes an inner contour and an outer contour of the part.

[0025] In step S1, the powder spreading thickness H is 20 microns to 180 microns. The ultrafast laser is a femtosecond or picosecond laser.

[0026] Combined with Figures 2 to 6As shown, after a powder doctor blade spreads a layer of metal powder (which can also be non-metal powder, such as ceramic powder, polymer material powder, or multi-metal mixed powder, etc.) with a thickness of H, a shaping laser melts out the shape of the part on the powder. Then, an ultrafast laser is used to directly scan the inner contour or the inner and outer contours on the printed shape of this layer in-situ to achieve a subtractive effect. The number of scans of the contour can be one or multiple according to needs; Furthermore, according to the appropriate subtractive thickness h tested previously, the lifting mechanism at the bottom of the forming chamber raises the entire part by h, so that the position that could not be "cut" by the part before is raised within the effective focal length of the ultrafast laser, enabling efficient removal of the next layer; the mechanism raises the part position by h again, and uses the ultrafast laser to subtract the contour again until the total raised height h t =h n *n (n is the number of ascents) is greater than the additive height H, then the subtractive process ends, or after multiple times, or after multiple times, the lifting mechanism raises the part position by h again, and uses the ultrafast laser to subtract the contour again until the total raised height h t =h n *n (n is the number of ascents) is greater than the additive height H, then the subtractive process ends. Or after multiple times, the lifting mechanism raises the part position by h again, and uses the ultrafast laser to subtract the contour again until the total raised height h t =h n *n (n is the number of ascents) is greater than the additive height H, then the subtractive process ends.

[0027] After the ultrafast laser scans the layer once or multiple times, the lifting mechanism raises the part position by h again, and uses the ultrafast laser to subtract the contour again until the total raised height h t =h n *n (n is the number of ascents) is greater than the additive height H, then the subtractive process ends. At this time, the lifting mechanism lowers the entire part by h n +H height, and then the powder spreading knife spreads the powder with a height of H on the surface of the part, preparing for the additive process of the next layer, and so on in a cycle until the entire part printing process ends.

[0028] During the above additive and subtractive processes, when H and h are not in a divisible relationship, the total raised height h t should be greater than H. That is, assuming the powder spreading thickness is 50 microns and the effective subtractive depth is 20 microns, after printing one layer, the lifting mechanism will rise 3 times, that is, after achieving 20 microns * 3 layers = 60 microns > 50 microns powder spreading thickness, the subtractive step of this layer ends, and the lifting mechanism lowers 60 + 50 = 110 microns, waiting for the powder spreading of the next layer.

[0029] After printing the component based on the above method, take it out of the 3D printing device.

[0030] Compared with the prior art, the present invention is realized based on a multi-laser additive and subtractive manufacturing process. The additive process is the same as the principle of traditional SLM. The difference is that after each layer of printing is completed, one or more ultrafast laser optical modules will be enabled to scan the edge of the printed shape to achieve subtractive processing. The purpose is to reduce the staircase effect between layers, thereby reducing the surface roughness of the part.

[0031] The above are only preferred embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements or improvements made within the technical scope of the present invention shall be included within the scope protected by the present invention.

Claims

1. A powder spreading type multi-laser additive and subtractive composite manufacturing method, characterized in that, It includes the following steps: Step S1: Use the powder doctor blade of the metal selective laser melting printing equipment to spread metal powder with a thickness of H on the substrate; Step S2: Use the forming laser to melt out the part shape contour on the powder; Step S3: Use the ultrafast laser to perform in-situ scanning on the part shape contour; Step S4: According to the pre-tested material removal thickness h, control the lifting mechanism at the bottom of the forming chamber of the metal selective laser melting printing equipment to drive the substrate to rise as a whole by h, and raise the position where the part shape in Step S3 is not cut to within the effective focal length range of the ultrafast laser; Step S5: After the current layer is scanned one or more times by an ultrafast laser, the lifting mechanism at the bottom of the forming chamber drives the substrate to rise as a whole by h again, and the ultrafast laser is used again to perform material subtraction on the part shape contour. Repeat Step S5 until the total height h t risen by the substrate is greater than the additive height H, then the material subtraction ends. Among them, h t = h n * n, where n is the number of rises; Step S6, the lifting mechanism at the bottom of the forming chamber drives the substrate to lower by another height h n +H, the powder doctor blade spreads a layer of metal powder with a thickness of H on the substrate to perform the additive process for the next layer; Repeat Steps S1 to S6 until the entire part printing process ends.

2. The powder spreading type multi-laser additive and subtractive composite manufacturing method according to claim 1, wherein In Step S1, the metal selective laser melting printing equipment includes an inert gas protected printing space, and the substrate is located in the inert gas protected printing space.

3. The powder spreading type multi-laser additive and subtractive composite manufacturing method according to claim 1, wherein, In Step S1, the metal powder can be a non-metal powder or a multi-metal mixed powder.

4. The powder spreading type multi-laser additive and subtractive composite manufacturing method according to claim 1, wherein, In Step S2, the part shape contour includes an inner contour and an outer contour of the part.

5. The powder spreading type multi-laser additive and subtractive composite manufacturing method according to claim 1, characterized in that, In Step S1, the powder spreading thickness H is 20 microns to 180 microns.

6. The powder spreading type multi-laser additive and subtractive composite manufacturing method according to claim 1, characterized in that The ultrafast laser is a femtosecond or picosecond laser.

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