Horizontal support-free forming method for laser powder bed melting

Abstract

The invention provides a support-free forming method for laser powder bed melting, and relates to the technical field of metal additive manufacturing, and the horizontal support-free forming method for laser powder bed melting comprises the following steps: S1, printing a first-layer support-free overhanging surface by using an out-of-focus laser beam, so that a first-layer metal powder is in a sintering state, and a first-layer sintering layer is formed; s2, printing a predetermined number of layers of support-free overhanging surfaces layer by layer by using an out-of-focus laser beam, melting each new printing layer, remelting the previous printing layer, and avoiding remelting to the lower surface of the first sintering layer; and S3, after printing of the support-free overhanging surface with the preset number of layers is completed, subsequent layer printing is conducted. The first sintering layer is printed by using the out-of-focus laser beam, so that a supporting foundation is provided for a subsequent overhanging structure, and the problem of collapse of the first layer is avoided. Fusion and combination of each new printing layer and the previous printing layer are controlled, remelting to the lower surface of the first layer is avoided, the upper surface and the lower surface which are not supported are smooth, and powder adhesion is avoided.

Description

Technical Field

[0001] The invention relates to the technical field of metal additive manufacturing, and in particular to a horizontal unsupported forming method of laser powder bed melting. Background Art

[0002] Laser powder bed fusion (LPBF) technology shows great potential in manufacturing parts with complex geometries, especially in the aerospace, medical and automotive fields.

[0003] However, LPBF technology faces challenges in manufacturing parts with overhanging structures, such as bridge-like structures or structures with an inclination angle less than 45°. These overhanging structures are prone to deformation and collapse during the printing process, resulting in printing failure or substandard part quality.

[0004] In order to support these overhanging structures, traditional LPBF processes usually require the addition of support structures. However, the design and removal of support structures not only increase printing time and material consumption, but also leave marks on the surface of the parts, requiring additional post-processing steps, increasing manufacturing costs and complexity.

[0005] Therefore, it is necessary to develop an LPBF forming method that can stably print overhanging structures without a supporting structure to overcome the defects of the existing technology. Summary of the invention

[0006] In order to overcome the problems existing in the related art, the purpose of the present invention is to provide a support-free forming method of laser powder bed fusion, which provides a support basis for the subsequent overhanging structure by using a defocused laser beam to print the first sintered layer, controls the melting and bonding of each new printed layer with the previous printed layer, and avoids remelting to the lower surface of the first layer, so that the upper and lower surfaces of the support are flat and powder is avoided. This overcomes the problem of the need for a support structure in the prior art.

[0007] A support-free forming method of laser powder bed fusion, comprising:

[0008] Step S1: using a defocused laser beam to print the first layer of unsupported overhanging surface, so that the first layer of metal powder is in a sintered state to form a first sintered layer;

[0009] Step S2: using a defocused laser beam to print a predetermined number of unsupported overhanging surfaces layer by layer, so that each new printed layer is melted and the previous printed layer is remelted, and remelting to the lower surface of the first sintered layer is avoided;

[0010] Step S3: After completing the printing of the predetermined number of layers of unsupported overhanging surfaces, subsequent layer printing is performed.

[0011] The first layer of metal powder is sintered by a defocused laser beam to form a first sintered layer with a certain strength but not completely dense, and then the predetermined number of layers are printed layer by layer by a defocused laser beam and remelted with the previously printed layer, and finally the subsequent layers are printed. The sintered layer provides initial support, and the layer-by-layer remelting ensures the interlayer metallurgical bonding and overall strength of the overhanging structure; the setting of the predetermined number of layers ensures the stability of the overhanging part during the subsequent printing process.

[0012] Preferably, the sintered state refers to the formation of sintered necks between metal powders, while the whole is not completely melted into a liquid state.

[0013] This sintered state enables a certain connection strength to be formed between the first layer of metal powder particles, which is sufficient to support subsequent printing layers, while avoiding collapse or deformation caused by complete melting, thereby ensuring the stability of the first layer structure and laying the foundation for subsequent support-free printing.

[0014] Preferably, the predetermined number of layers is at least three layers.

[0015] The purpose of setting the predetermined number of layers is to form a foundation of an overhang structure with sufficient strength and stability before gradually transitioning to normal laser melting printing. The setting of at least three layers can ensure that the number of melted layers will not be too small to cause the structure to collapse before forming a solid overhang structure.

[0016] Preferably, the defocus amount of the defocused laser beam is positive defocus.

[0017] Printing is performed using a positive defocused laser beam. Positive defocusing can expand the laser spot and reduce the laser energy density, thereby achieving powder sintering, avoiding powder splashing and molten pool instability caused by excessive energy input, and is conducive to forming a uniform and dense sintered layer, providing a stable foundation for subsequent support-free printing.

[0018] Preferably, the step S2 also includes controlling the size and distribution of interlayer pores.

[0019] Precisely controlling the interlayer pores can effectively release the residual stress generated during the printing process, reduce deformation and warping, and improve the forming accuracy and mechanical properties of the overhanging structure.

[0020] Preferably, the controlling of the interlayer pores specifically includes adjusting laser power, scanning speed, and scanning spacing.

[0021] The interlayer pores can be controlled by adjusting the laser power, scanning speed and scanning spacing. These three parameters directly affect the laser energy input and the size of the molten pool, so that the size and distribution of the interlayer pores can be accurately controlled, achieving effective regulation of residual stress.

[0022] Preferably, in step S2, the laser power of the laser beam is increased layer by layer.

[0023] As the number of layers increases, the weight of the overhanging part also increases. Increasing the laser power layer by layer can ensure that each layer has sufficient energy input to ensure the quality of melting and bonding, while avoiding deformation and collapse caused by excessive energy in the first few layers.

[0024] Preferably, in step S3, a non-defocused laser beam is used for printing the subsequent layers.

[0025] Use a non-defocused laser beam for subsequent layer printing. After the predetermined number of layers of unsupported overhang structure printing is completed, the overhang structure has sufficient strength and stability. At this time, a non-defocused laser beam can be used for normal laser melting printing to improve printing efficiency and forming quality.

[0026] Preferably, the metal powder material is titanium alloy powder, nickel alloy powder, aluminum alloy powder or stainless steel powder.

[0027] Preferably, the metal powder material is Ti6Al4V.

[0028] The beneficial effects of the present invention are:

[0029] The present invention provides a support-free forming method of laser powder bed melting. The horizontal support-free forming method of laser powder bed melting provides a support basis for the subsequent overhanging structure by using a defocused laser beam to print the first sintered layer, thereby avoiding the problem of collapse of the first layer; and printing a predetermined number of layers of support-free overhanging surfaces layer by layer, and controlling the melting and bonding of each new printed layer with the previous printed layer, and avoiding remelting to the lower surface of the first layer, thereby ensuring the stable construction and high-quality forming of the overhanging structure; finally, after completing the printing of the predetermined number of layers, subsequent layers are printed to achieve support-free manufacturing of the entire part. No additional support structure is required, thereby simplifying the printing process, shortening the manufacturing cost and post-processing time, and improving production efficiency; at the same time, since the removal of the support structure is avoided, the surface quality of the part is also improved, making the upper and lower surfaces of the support-free flat and avoiding powder sticking. It can also manufacture more complex geometric shapes, expanding the application scope of laser powder bed melting technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a flow chart of the horizontal unsupported forming method of laser powder bed fusion provided in the present application;

[0031] Figure 2 It is the spot size and energy distribution diagram under different defocus amounts provided in this application;

[0032] Figure 3 It is a schematic diagram of thermal effects under defocus conditions provided in this application;

[0033] Figure 4 is a schematic diagram of a semi-trapezoidal unsupported model provided in Example 1 of the present application;

[0034] Figure 5 This is a physical picture of the unsupported first layer after printing provided in Example 1 of the present application;

[0035] Figure 6 This is a physical picture of the effect after the unsupported two-layer printing provided in Example 1 of the present application;

[0036] Figure 7 This is a physical picture of the sheet after three or four layers of printing without support provided in Example 1 of the present application;

[0037] Figure 8 It is a schematic diagram of the bridge-type unsupported model provided in Example 2 of the present application. DETAILED DESCRIPTION

[0038] The preferred embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although the preferred embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to make the present invention more thorough and complete, and to fully convey the scope of the present invention to those skilled in the art.

[0039] Example 1

[0040] like Figure 1-Figure 7 As shown, this embodiment provides a horizontal unsupported forming method of laser powder bed fusion, and the horizontal unsupported forming method of laser powder bed fusion includes:

[0041] Step S1: Use a defocused laser beam to print the first layer of unsupported overhanging surface, so that the first layer of metal powder is in a sintered state to form a first sintered layer; the sintered state refers to the formation of sintering necks between the metal powders, while the whole is not completely melted into a liquid state.

[0042] Step S2: Use a defocused laser beam to print a predetermined number of unsupported overhanging surfaces layer by layer, adjust the laser power, scanning speed, scanning spacing, control the size of the interlayer pores, melt each new printed layer and remelt the previous printed layer, and avoid remelting to the lower surface of the first sintered layer; the predetermined number of layers is at least three. The laser power of the laser beam increases layer by layer.

[0043] Step S3: After completing the printing of a predetermined number of layers of unsupported overhanging surfaces, subsequent layer printing is performed, and the subsequent layer printing adopts a non-defocused laser beam.

[0044] The defocus amount of the defocused laser beam is positive defocus.

[0045] The metal powder material is titanium alloy powder, nickel alloy powder, aluminum alloy powder or stainless steel powder. In this embodiment, the metal powder material is Ti6Al4V.

[0046] More specifically, the following steps may be included:

[0047] The energy distribution of the continuous Gaussian laser of the institute's printing equipment, and the energy distribution of the Gaussian laser after using different defocus amounts. The defocus is positive, and the positive defocus operation is to lower the printing plane so that it is below the focal plane, which is convenient for the approximate control of the laser energy input in the subsequent printing process, so as to study the parameters of the unsupported first layer printing.

[0048] The LPBF printing equipment is equipped with a continuous Gaussian laser, which can precisely control the laser power, scanning speed, scanning spacing and defocus. The equipment needs to have a stable powder laying system and a precise platform control system.

[0049] Using a defocused continuous laser to print the first layer of unsupported overhanging surface, the laser parameter input can be quickly adjusted to obtain lower laser energy, so that the first printed layer is in a powder sintering state. Powder sintering is defined as the occurrence of neck connection between powders without the whole powder liquefying or melting. The entire printing process is carried out under the protection of an inert gas (such as argon) to prevent oxidation of the metal powder.

[0050] Before printing, the laser energy distribution of the equipment used needs to be studied in detail, including the energy distribution under different defocusing amounts. This embodiment uses positive defocusing, that is, the printing plane is placed below the focal plane, so as to better control the laser energy input and avoid over-melting and deformation. The optimal defocusing amount is determined by experiment, which is 5 mm in this example.

[0051] The sintered state can serve as a pre-support for the second layer printing, because powder sintering provides enough space to buffer the deformation caused by residual stress.

[0052] In addition, powder sintering at lower energy input is less prone to powder sticking problems, which helps to form a lower surface with consistent surface roughness.

[0053] A gradient printing strategy is adopted to gradually increase the input energy, and the second layer of unsupported overhanging surface is printed using a defocused continuous laser. After the unsupported first layer is sintered, the forming cylinder is lowered by a layer thickness to perform normal powder laying.

[0054] By adjusting parameters such as laser power, scanning speed and scanning spacing to control the input of laser energy, the second layer of unsupported overhanging surface is printed so that the second layer of overhanging surface just remelts the first layer of sintered layer, avoiding the remelting of the lower surface of the first layer, keeping the lower surface in a relatively flat state, and selecting a relatively flat upper surface as the best printing parameter for the second layer.

[0055] The unsupported LPBF forming process parameters for the third and fourth layers can refer to the second layer process window.

[0056] Due to the adoption of the gradient printing strategy, the process selection range can be narrowed down according to the forming rules of the second layer and the input energy can be gradually increased. The energy input for the third layer of support-free printing is similar to that of the second layer. It is necessary to just melt the second layer and the first sintered layer, keep the lower surface in a relatively flat state, and make the upper surface flat.

[0057] The fourth layer is similar to the previous layers in principle. Attention should be paid to the smooth printing of the overhanging surfaces of the third and fourth layers. The key lies in the precise control of the pores between layers. A certain amount of pores can be maintained to buffer the displacement caused by residual stress, thereby reducing warping.

[0058] After precise energy control of the first four unsupported printing layers, a horizontal unsupported structure with good rigidity and relatively flat upper and lower surfaces can be obtained.

[0059] The interlayer pores can be controlled by adjusting the laser energy density. The laser energy density is related to the laser power, scanning speed, scanning spacing and powder layer thickness. These pores help to buffer the residual stress deformation caused by thermal gradient.

[0060] The number of interlayer pores can be adjusted by laser energy density and defocused sintering. When there are too many pores in the first few layers of overhang, it is not conducive to the subsequent printing of dense structures. Laser can be used to remelt the solid parts of the upper layers to reduce the internal pores, but the laser energy input needs to be controlled. If the laser energy input is further increased, it will cause serious warping, and even the laser will penetrate into the lower layer, causing powder sticking. The porosity needs to be adjusted below 10% to ensure density while buffering the residual stress deformation caused by thermal gradient through pores. The energy density formula is as follows:

[0061]

[0062] Where E is the energy density (J / mm 3 ), P is the laser power (W), V is the scanning speed (mm / s), H is the hatch spacing (mm), and D is the layer thickness (mm).

[0063] The subsequent printing layers can be printed normally through non-defocusing, but the energy range of the subsequent non-defocusing must also be controlled until the printing is successful.

[0064] In this embodiment, the processed unsupported model is a semi-trapezoidal model. According to the above-mentioned unsupported forming method of laser powder bed melting, the approximate energy range after defocusing is first determined. The defocus distance is 5 mm, the fixed layer thickness is 30 microns, and the powder material is Ti6Al4V. For the printing of the first layer, the low energy input is controlled so that the first layer is a sintered layer.

[0065] The second layer gradually increases the input energy so that the second layer just melts the first layer without damaging the lower surface of the first layer. At this time, the upper and lower surfaces without support are relatively flat, and there is no sticky powder. Figure 4 The third and fourth layers are printed similarly to the second layer.

[0066] By adjusting parameters such as laser power, scanning speed, and scanning spacing, the input of laser energy is controlled to complete the printing of subsequent layers, so that a flat sheet is formed in the unsupported area. The specific parameters are shown in Table 1.

[0067] Table 1

[0068] Number of layers Laser power Scan speed Defocus Scanning distance First floor 20W 800mm / s 5mm 100μm Second floor 20W 600mm / s 5mm 100μm Third floor 40W 600mm / s 5mm 100μm Fourth floor 60W 600mm / s 5mm 100μm Subsequent layers 80W 200mm / s 0mm 100μm

[0069] The horizontal unsupported forming method of laser powder bed melting provided in this embodiment successfully realizes the unsupported forming of horizontal semi-trapezoidal structures by adopting a gradient printing strategy of defocused laser sintering combined with incremental energy melting layer by layer. This method effectively avoids the difficulty of removing traditional support structures, simplifies the post-processing process, and reduces manufacturing costs and time. At the same time, by controlling the interlayer porosity, the residual stress is effectively buffered, and the dimensional accuracy and surface quality of the formed parts are improved.

[0070] Example 2

[0071] Example 2: Bridge-type support-free printing

[0072] The horizontal unsupported forming method of laser powder bed fusion provided in this example is applied to bridge-type unsupported printing, such as Figure 8 As shown in the figure, the printing parameters of the bridge structure are similar to those of the semi-trapezoidal structure, but they need to be fine-tuned according to the span and geometry of the bridge. The horizontal support-free forming method of laser powder bed fusion includes:

[0073] Step S1: using a defocused laser beam to print the first layer of unsupported overhanging surface, so that the first layer of metal powder is in a sintered state to form a first sintered layer;

[0074] Step S2: using a defocused laser beam to print a predetermined number of unsupported overhanging surfaces layer by layer, so that each new printed layer is melted and the previous printed layer is remelted, and remelting to the lower surface of the first sintered layer is avoided;

[0075] Step S3: After completing the printing of the predetermined number of layers of unsupported overhanging surfaces, subsequent layer printing is performed.

[0076] The processing parameters of each layer are shown in Table 2. The first layer is the same as in Example 1, forming a sintered layer.

[0077] The parameters of the second and third layers are similar to those of the second layer in Example 1, but require lower energy input to avoid premature melting and resulting in bridge collapse.

[0078] The fourth level of power boost ensures the stability and strength of the bridge.

[0079] Subsequent layers are compacted using a non-defocused laser beam. The substrate can also be preheated, which can reduce thermal gradients and minimize deformation.

[0080] Table 2

[0081] Number of layers Laser power Scan speed Defocus Scanning distance First floor 20W 800mm / s 5mm 100μm Second floor 20W 600mm / s 5mm 100μm Third floor 20W 600mm / s 5mm 100μm Fourth floor 40W 600mm / s 5mm 100μm Subsequent layers 80W 200mm / s 0mm 100μm

[0082] The horizontal unsupported forming method of laser powder bed fusion provided in this embodiment applies the gradient printing strategy to the unsupported forming of bridge-type structures. By adjusting the laser parameters and the interlayer fusion strategy, the stable construction of a bridge-type structure with a large span is achieved without the need for additional support structures. This not only simplifies the manufacturing process, but also expands the application scope of laser powder bed fusion technology in the manufacture of parts with complex geometric shapes, providing a new solution for the efficient and high-precision manufacture of challenging structures.

[0083] Unless otherwise specifically stated, the relative arrangement, numerical expressions and numerical values ​​of the parts and steps set forth in these embodiments do not limit the scope of the application. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a restriction. Therefore, other examples of exemplary embodiments can have different values. It should be noted that similar reference numerals and letters represent similar items in the following drawings, and therefore, once a certain item is defined in an accompanying drawing, it does not need to be further discussed in the subsequent accompanying drawings.

[0084] In addition, it should be noted that the use of terms such as "first" and "second" to limit is only for the convenience of distinction. Unless otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of this application.

[0085] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A horizontal unsupported forming method of laser powder bed fusion, characterized in that: include: Step S1: using a defocused laser beam to print the first layer of unsupported overhanging surface, so that the first layer of metal powder is in a sintered state to form a first sintered layer; Step S2: using a defocused laser beam to print a predetermined number of unsupported overhanging surfaces layer by layer, so that each new printed layer is melted and the previous printed layer is remelted, and remelting to the lower surface of the first sintered layer is avoided; Step S3: After completing the printing of the predetermined number of layers of unsupported overhanging surfaces, subsequent layer printing is performed.

2. The horizontal unsupported forming method of laser powder bed fusion according to claim 1, characterized in that: The sintered state refers to the formation of sintered necks between metal powders, while the whole is not completely melted into a liquid state.

3. The horizontal unsupported forming method of laser powder bed fusion according to claim 1, characterized in that: The predetermined number of layers is at least three layers.

4. The horizontal unsupported forming method of laser powder bed fusion according to claim 1, characterized in that: The defocus amount of the defocused laser beam is positive defocus.

5. The horizontal unsupported forming method of laser powder bed fusion according to claim 1, characterized in that: The step S2 also includes controlling the size of the pores between the layers.

6. The horizontal unsupported forming method of laser powder bed fusion according to claim 5, characterized in that: The controlling of the interlayer pores specifically includes adjusting the laser power, scanning speed, and scanning spacing.

7. The horizontal unsupported forming method of laser powder bed fusion according to claim 1, characterized in that: In step S2, the laser power of the laser beam is increased layer by layer.

8. The horizontal unsupported forming method of laser powder bed fusion according to claim 1, characterized in that: In step S3, the subsequent layer printing uses a non-defocused laser beam.

9. The horizontal unsupported forming method of laser powder bed fusion according to claim 1, characterized in that: The metal powder material is titanium alloy powder, nickel alloy powder, aluminum alloy powder or stainless steel powder.

10. The horizontal unsupported forming method of laser powder bed fusion according to claim 9, characterized in that: The metal powder material is Ti6Al4V.

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