Selective laser sintering method, 3D printing method and application thereof

Abstract

The invention discloses a high-efficiency selective laser sintering method, which comprises at least one mixture of raw material powder including a low-melting-point binder and at least one laser beam for selective laser sintering; the melting point of the binder is m p , the decomposition temperature is b p , so that the laser beam irradiates the raw material of the mixture, the highest temperature of the raw material rises to T, the duration of the temperature is t, and the following conditions are met: #imgabs0# and m p <T<b p , t>0; this method allows the temperature of a larger range of raw material powder to be maintained in the range from melting point to decomposition point for a certain period of time, while making the temperature distribution and gradient tend to be uniform, so that the residual stress and deformation after laser sintering are smaller; and the beam irradiation with a larger irradiation area also ensures the improvement of laser sintering efficiency.

Description

Technical Field

[0001] The present invention relates to the field of additive manufacturing, and in particular to a selective laser sintering method, a 3D printing method and applications thereof, and is particularly applicable to the field of additive manufacturing of large-scale building structures. Background Art

[0002] Additive manufacturing is a new manufacturing process that emerged in the 1980s and integrates computers, machinery, materials and processing. Selective laser sintering (SLS) is an important branch of additive manufacturing. Its principle is to first place the raw material powder to be processed on the work surface. According to the cross-sectional information of the three-dimensional part, the laser spot scans the powder material in the area along the scanning path set by the computer, so that the raw material powder in the area is melted and bonded together, and then the powder is re-spread and the above steps are repeated. The material is stacked layer by layer to obtain the required three-dimensional part. This method has the advantages of high raw material utilization and the ability to form components of any complex shape. It is widely used in aerospace, automobiles, military weapons, biomedicine and other fields. Nevertheless, with the rapid development of aerospace technology and weapons and equipment, higher requirements are put forward for the forming efficiency and forming quality of additive manufacturing technology, especially for architectural structures, which have very high requirements for printing efficiency.

[0003] In order to achieve high-precision manufacturing, the currently used SLS technology mainly uses a small spot laser beam. Under high power density, a small spot (0.03mm-0.1mm) laser beam is used to quickly laser scan the raw material powder. This results in a small surface area of ​​the raw material melted per unit time, and the molding efficiency is low when printing and manufacturing large parts. At the same time, due to the small laser beam spot, the conventional laser beam energy is Gaussian distributed, so the raw material is heated in a small temperature range, resulting in a large thermal temperature gradient in the region, which is easy to cause large residual stress and deformation; and the excessive temperature rise rate is easy to cause defects such as holes in the powder spheroidization, which ultimately reduces the dimensional accuracy and mechanical properties of the parts. Moreover, for the manufacture of some heat-resistant alloys, quality problems such as cracking are very likely to occur.

[0004] Patent CN103358555 discloses a multi-beam laser scanning processing method, which uses multiple laser beams to simultaneously process raw material powder during printing and sintering to improve printing efficiency. Patent 201680034015.7 discloses an additive manufacturing method using multiple beams, which uses multiple beams to expand the overall molding format of the part, but does not improve the molding efficiency of a single format. Patent 201310670777.4 discloses a laser selective melting SLM device and processing method based on four laser duplex stations, which uses a distributed scanning strategy to first use a low-power density laser beam to scan the edge, and then use a large spot high-power density laser beam to scan the center area. In this method, the two beams are not performed simultaneously, which to a certain extent limits the further improvement of printing efficiency. Patent CN112091213 discloses an additive manufacturing method that utilizes a high-power light beam and a low-power light beam to switch with each other. The low-power light beam is used to ensure high efficiency, while the high-power light beam is used to ensure high precision. Although this method can take into account both efficiency and precision to a certain extent, the efficiency is still limited to a certain extent because the two light beams work in staggered order, and the coordination of the two light beams is difficult to control.

[0005] At present, the field basically adopts the method of multiple beams or large spots to improve efficiency. In order to meet the requirements of accuracy, the method of matching small spot with high power density beam is adopted. However, the current methods are relatively complicated and the efficiency is still limited to a certain extent.

[0006] Therefore, there is an urgent need in the art for a manufacturing method that can improve printing efficiency, reduce costs, and reduce residual stress and deformation. Especially under conditions such as additive manufacturing to construct houses, manufacturing efficiency and quality are particularly important. Summary of the invention

[0007] In order to achieve the above objectives, in view of the shortcomings of the prior art, the present invention proposes a selective laser sintering method to solve the problems of low efficiency and poor quality in additive manufacturing.

[0008] To achieve the above object, the present invention provides a selective laser sintering method, comprising the following steps:

[0009] providing at least a raw material powder mixture including a low melting point binder, and at least one laser beam for selective laser sintering;

[0010] The laser beam is irradiated to the raw materials of the mixture to melt the binder and bond the mixture;

[0011] The melting point of the binder is m p , the decomposition temperature is b p, the laser beam is irradiated on the raw material of the mixture, the maximum temperature of the raw material is T, the duration of the maximum temperature is t, and the following conditions are met:

[0012] And m p <T<b p , t>0;

[0013] In a preferred embodiment, the time t≥1.2s;

[0014] In a preferred embodiment, the maximum temperature is 100°C≤T≤550°C;

[0015] In a preferred embodiment, the laser beam irradiates the surface of the mixture material to form a region with a surface area S, where S ≥ 1 mm 2 ,

[0016] The laser beam irradiation power level is P, and P / S ≤ 10w / mm 2 .

[0017] In a preferred example, the shape of the area formed by the laser beam irradiating the surface of the raw material powder is a circular outline or an elongated rectangular outline, the diameter of the circular outline is d, and the long side of the rectangular outline is L.

[0018] In a preferred embodiment, the energy of the laser beam irradiation area has a circular, Gaussian distribution;

[0019] In a preferred embodiment, the laser beam has uniform energy distribution in the irradiated area;

[0020] In a preferred embodiment, the laser beam processes the raw material in a scanning manner, and the scanning speed is V, satisfying d / 5≤V≤2*d and L / 5≤V≤2*L.

[0021] In a preferred example, the binder is a thermoplastic resin.

[0022] The present invention also provides a 3D printing method based on selective laser sintering, in which the mixture obtained by the selective laser sintering method is bonded and stacked in a layer-by-layer manner to obtain an integral component.

[0023] The present invention also provides the application of the mixture bond obtained by the selective laser sintering method in 3D printing.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] In order to achieve higher efficiency of raw material powder during laser sintering, the present invention adopts a laser beam with a larger irradiation spot during laser sintering, so that the raw material in a larger range is subjected to heat, the temperature rises slowly, and a uniform temperature field distribution is obtained in a larger range, thereby overcoming processing defects. At the same time, the laser beam in the area maintains a smaller power density, so that the raw material is kept in a molten state for a certain period of time, which can ensure that the raw material powder in a larger range is maintained within a uniform temperature field range, so that the residual stress and deformation of the component after processing are smaller, and the sintering quality is improved; at the same time, since the laser beam irradiation area is larger, the processing efficiency is higher; since only one laser beam is used, the requirement for laser power density is lower, so the overall cost is also lower. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other alternative implementation methods can be obtained based on these drawings without paying creative work.

[0027] Figure 1 It is a schematic diagram of the process of the present invention.

[0028] Figure 2 It is a schematic diagram of the printing process of the integral component in the present invention.

[0029] Figure 3 The figure is a schematic diagram of a light beam distribution and a printing area involved in the present invention.

[0030] Figure 4 The figure is a schematic diagram of a light beam distribution and a printing area involved in the present invention.

[0031] Figure 5 The figure is a schematic diagram of a light beam distribution and a printing area involved in the present invention.

[0032] Figure 6 The figure is a schematic diagram of a light beam distribution and a printing area involved in the present invention.

[0033] Figure 7 The figure is a schematic diagram of a light beam distribution and a printing area involved in the present invention.

[0034] Figure 8 The figure is a schematic diagram of a light beam distribution and a printing area involved in the present invention.

[0035] Fig. 9 The figure is a schematic diagram of a light beam distribution and a printing area involved in the present invention.

[0036] Fig.10The figure is a schematic diagram of a light beam distribution and a printing area involved in the present invention.

[0037] Fig.11 The figure is a schematic diagram of a light beam distribution and a printing area involved in the present invention.

[0038] Fig.12 A printing scanning strategy involved in the present invention is a schematic diagram of a laser beam scanning along a straight line.

[0039] Fig.13 A schematic diagram of a printing strategy involved in the present invention is a laser beam traveling in a stamping manner.

[0040] Fig.14 Another schematic diagram of a printing strategy involved in the present invention in which a laser beam travels in a stamping manner.

[0041] Fig.15 Schematic diagram of beam distribution when the laser beam is Gaussian distributed in the traditional method.

[0042] Fig.16 Schematic diagram of beam distribution when the laser beam used in the method of the present invention is uniformly distributed.

[0043] Fig.17 Another component is laser printed using the method of the present invention.

[0044] Fig.18 Another component is laser printed using the method of the present invention.

[0045] Fig.19 Another component is laser printed using the method of the present invention.

[0046] Fig. 20 The components and defects printed by laser using traditional methods.

[0047] Figure numerals, 1-laser beam, p1-first layer printing structure, p2-second layer printing structure, p3-third layer printing structure, p4-fourth layer printing structure, pn-nth layer printing structure, 2-irradiation area formed by the laser beam on the surface of the raw material, 3-raw material mixture, L-length of the laser beam irradiation area when it is a rectangle, B-width of the second laser beam irradiation area when it is a rectangle, d-diameter of the second laser beam irradiation area when it is a circle. DETAILED DESCRIPTION

[0048] After extensive and in-depth research, the inventors discovered a selective laser sintering method with beneficial effects, and completed the present invention on this basis.

[0049] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, the accompanying drawings are schematic diagrams, so the device and apparatus of the present invention are not limited by the size or ratio of the schematic diagrams.

[0050] It should be noted that in the claims and description of this patent, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "including one" do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0051] Reference now Figure 1 The method of the present invention is a selective laser sintering method for powder material additive manufacturing. First, at least one printing raw material powder is provided, and the powder is evenly mixed with a binder to form a mixture 3, and then the powder is spread, and then the binder is melted and the powder is bonded into shape by a method based on a special laser beam to control the heat input. According to the component shape input by the computer, the laser beam is used to repeat the above steps to print p1, p2, p3, p4 to pn layer by layer to form the required component, such as Figure 2 As shown. In the present invention, the printing raw materials include one or more of plastic, metal powder and ceramic powder. The binder is generally an organic binder with a low melting point. The main components are nylon powder, phenolic resin, epoxy resin, stearic acid, fly ash and other components. It also includes thermoplastic polymers such as polyetheretherketone (PEEK), polyetherketone (PEK), polyetherketoneketone (PEKK), polyetheretherketoneketone (PEEKK) and polyetherketoneetherketoneketone (PEKEKK), specifically a polymer with a long carbon chain or a short carbon chain. The melting point of the binder is m p , the decomposition temperature is b p .

[0052] The laser beam 1 has a wavelength of 0.3-10 μm, especially 0.5-3 μm infrared laser emission, which is common in SLS processing. The laser it emits can correspond to various types, including but not limited to solid-state lasers, direct diode lasers, photonic crystal lasers, semiconductor lasers, gas lasers, chemical lasers, excimer lasers or free electron lasers. The laser can be a continuous laser or a pulsed laser, and its peak power is generally 50w-10000w, especially 100w-5000w. The laser beam 1 is generally an initial laser beam emitted by a laser and transmitted through an optical fiber or an optical element.

[0053] When the laser beam 1 is irradiated to the surface of the mixture material 3, an irradiation area 2 is formed. The irradiation area 2 has a surface area, and its shape can include various types; Figure 3 The shape is rectangular, having a length L and a width B, and in particular a square shape, such as Figure 4 shown. Figure 5 As shown, the shape of the laser beam irradiation area is circular, i.e., a circular spot, having a diameter d; Figure 6 It is shown that the shape of the laser beam irradiation area is an ellipse with a major axis and a minor axis; Figure 7 The laser beam irradiation area is shown as a polygonal free-form shape consisting of multiple straight lines and free curves; the irradiation shape can also be, for example Figure 8 The irradiation area shown has a ring-shaped morphology, and the light beam forms a ring surrounded by concentric circles along the outer circle; Fig. 9 Shown by Figure 8 The composite morphology of the composite irradiation area composed of the ring and the central circle shown in FIG. ; In addition, the irradiation area morphology can also be composed of a combination of the above multiple shapes, such as Fig.10 The shape shown is a combination of rectangle and ellipse. Fig.11 The figure shows a combination of multiple free closed curves. In particular, for an irradiation beam with a complex shape, the beam energy distribution of each individual area can be freely adjusted, such as the power ratio and the beam distribution form.

[0054] Generally, there are many types of laser beam scanning methods for each layer of laser printing, such as moving the laser beam along the mixed material at a certain speed V to melt and bond the raw materials in the scanning area together, such as Fig.12 As shown; it can also proceed in a stamping manner, that is, a laser beam with a certain spot size irradiates a certain area, and then transfers to the next area, so that the next area is also melted and bonded to finally form the entire workpiece, such as Fig.13 As shown, there are many ways to stamp, such as Fig.14It is shown that the next area can cover a partial area of ​​the previous area. Similarly, the area irradiated by the light beam can be the same or different each time the stamp is stamped.

[0055] When the laser beam 1 is irradiated onto the mixed material 3, its temperature will rise. The highest temperature of the raw material rises to T. The duration of the temperature is t, and the following conditions are met: And m p <T<b p , t>0; preferably t≥1.2s. In the present invention, this purpose is achieved by controlling the incident parameters of the laser beam; for example, by controlling the power of the laser beam, the beam irradiation area and the scanning speed v or the dwell time. When the raw material is printed in a scanning manner, the scanning speed is v, and d / 5≤V≤2*d and L / 5≤V≤2*L are satisfied, S≥1mm 2 ;P / S≤10w / mm 2 ; When printing in a stamping manner, the dwell time of each area is t≥0.5s, preferably t≥1s; and a temperature monitoring module may be provided on the laser processing equipment to monitor the maximum temperature of the processing area in real time, for example, by infrared temperature measurement. The maximum temperature is 100℃≤T≤500℃; In the present invention, the power p of the laser beam is not less than 100w, preferably 500w-100000w, more narrowly 600-5000w.

[0056] In order to improve the overall processing efficiency and processing quality, in the present invention, the area of ​​the beam irradiation area is not less than or equal to a square area with a side length of 1x1mm. On the one hand, a larger beam irradiation area can increase the overall printing speed, and on the other hand, the printing quality can be improved by controlling the beam distribution form; in the present invention, the beam energy is evenly distributed in the entire irradiation area, such as Fig.15 As shown, different from the traditional Gaussian distribution ( Fig.16 ), the uniform distribution of the light beam in the irradiated area can ensure that the printed material has a more uniform temperature field distribution in a larger range, the temperature gradient is smaller during printing, the residual stress and deformation after printing are smaller, and the printing quality is improved.

[0057] Example 1

[0058] Reference now Fig.17, which shows that the method of the present invention is used, and the laser beam spot shape is rectangular, the length and width are 45x45mm respectively, the laser beam energy is evenly distributed in the area, the laser beam is emitted by a semiconductor laser with a wavelength of 940-1060nm, the laser power is 600-1500w, the printing raw material is a mixture composed of SiO2, Al2O3, TiO2, etc., and the added binder is a thermoplastic resin of polyaryletherketone, with a melting point of about 310°C and a decomposition point of about 550°C; the mixing ratio is 20% by mass of the binder, and the laser beam processes the raw material in a scanning manner, and the scanning speed is 10-30mm / s. During the entire process, the infrared thermometer equipped on the laser processing equipment can monitor the temperature in a timely manner and control the laser beam to maintain the processing temperature on the surface of the raw material in the range of 480-500°C for 1.5-2s. The overall processing efficiency can reach about 2L / h for the component with a total size of approximately 45mm x 170mm x 40mm. In addition, the deformation degree of the overall material after processing is also very small, and no processing defects occur.

[0059] Example 2

[0060] Reference now Fig.18 , which shows that the method of the present invention is adopted, the laser beam spot shape is rectangular, the length and width are 10x10mm respectively, the laser beam energy is evenly distributed in the area, the laser beam is emitted by a semiconductor laser with a wavelength of 940-1060nm, the laser power is 100-300w, the printing raw material is a mixture composed of components such as SiO2, Al2O3, TiO2, etc., and the added binder is a nylon thermoplastic resin with a melting point of about 220℃ and a decomposition point of about 280℃; the mixing ratio is 20% by mass of the binder, the laser beam processes the raw material in a scanning manner, and the scanning speed is 15-25mm / s. During the whole process, the laser beam is controlled to maintain the processing temperature of the raw material surface in the range of 260-270℃ for at least 1.5-2s, and the entire size of the component is 40mm x 40mm x 40mm. The overall processing efficiency reaches about 400mL / h, and the deformation degree of the overall material after processing is also very small, and no processing defects occur.

[0061] Example 3

[0062] Reference now Fig.19, which shows that the method of the present invention is adopted, and the laser beam spot shape is rectangular, the length and width are 40x40mm respectively, the laser beam energy is evenly distributed in the area, the laser beam is emitted by a semiconductor laser with a wavelength of 940-1060nm, the laser power is 500w, the printing raw materials are SiO2, Al2O3, TiO2, etc., and the added binder is a thermoplastic resin of polyaryletherketone, with a melting point of about 310℃ and a boiling point of about 550℃; the mixing ratio is 20% by mass of the binder, the laser beam is irradiated in a fixed-point manner, and the light emission time of each point is 2s. During the whole process, the infrared thermometer equipped with the laser processing equipment can monitor the temperature in time, and control the laser beam to maintain the processing temperature on the surface of the raw material in the range of 500-520℃ for at least 2s, and the complex component with an entire size of 120mm x 200mm x 50mm is processed. The overall processing efficiency reaches about 2L / h, and the deformation degree of the overall material after processing is also very small, and no processing defects occur.

[0063] Comparative Example

[0064] Reference now Fig. 20 , which shows the use of the traditional method, using a circular laser beam spot shape with a diameter of 70μm, the laser beam energy in the area is Gaussian distribution, the laser beam is emitted by a semiconductor laser with a wavelength of 1064nm, the laser power is 10w, the printing raw material is a mixture of SiO2, Al2O3, TiO2 and other components, and the added binder is a thermoplastic resin of polyaryletherketone with a melting point of about 310℃ and a boiling point of about 550℃; the mixing ratio is 20% by mass of the binder, and the laser beam processes the raw material in a scanning manner, with a scanning speed of 200mm / s to process the entire component with a size of 20mm x 20mm x10mm. The overall processing efficiency is only about 15mL / h, and the material is greatly deformed all day after processing, and many processing defects such as splashes and holes appear.

Claims

1. A selective laser sintering method, characterized in that: providing at least one raw material mixture including a binder, and at least one laser beam for selective laser sintering; The laser beam irradiates the raw material mixture, so that the binder melts and the raw material mixture bonds, and the maximum temperature T and the duration t of the maximum temperature of the raw material mixture rise, satisfying the following conditions: And m p <T<b p , t>0 In the formula, m p is the melting point temperature of the binder, b p is the decomposition temperature of the binder.

2. A selective laser sintering method according to claim 1, characterized in that: The duration of the maximum temperature is t≥1.2s.

3. A selective laser sintering method according to claim 1, characterized in that: The maximum temperature of the mixed raw materials rises to 100°C≤T≤550°C.

4. A selective laser sintering method according to claim 1, characterized in that: The laser beam irradiates the surface of the raw material of the mixture to form a region with a surface area of ​​S, S ≥ 1mm 2 , the laser beam irradiation power level is P, and P / S≤10w / mm2.

5. A selective laser sintering method according to claim 4, characterized in that: The shape of the area formed by the laser beam irradiating the surface of the raw material of the mixture is a circular outline with a diameter of d or a rectangular outline with a long side of L.

6. A selective laser sintering method according to claim 1 or 4, characterized in that: The energy of the laser beam irradiation area has an annular Gaussian distribution.

7. A selective laser sintering method according to claim 1 or 4, characterized in that: The laser beam has uniform energy distribution in the irradiated area.

8. A selective laser sintering method according to claim 5, characterized in that: The laser beam processes the raw material in a scanning manner, and the scanning speed is V, satisfying d / 5≤V≤2*d and L / 5≤V≤2*L.

9. A selective laser sintering method according to claim 1 or 4, characterized in that: The binder is a thermoplastic resin.

10. A 3D printing method based on selective laser sintering, characterized in that: The mixture obtained by the selective laser sintering method according to any one of claims 1 to 9 is bonded and stacked in a layer-by-layer manner to obtain an integral component.

11. An application of a mixture bond obtained by the selective laser sintering method according to any one of claims 1 to 9 in 3D printing.

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