A printing method of dual laser modulation linewidth

Abstract

This invention discloses a dual-laser modulated linewidth printing method, belonging to the field of 3D printing technology. The method includes the following steps: setting two sets of elongated laser beams, each with a scanning width of D; dividing the pattern to be printed into several printing blocks, each block having a width no greater than D; when printing each block, modulating the power of the two sets of elongated laser beams to equal the power required to melt metal; synchronously scanning the two sets of elongated laser beams along the length of the printing block; and during the scanning process, adjusting the overlapping area of ​​the two sets of elongated laser beams according to the actual linewidth d at the current printing position, so that the width of the overlapping area is the same as the actual linewidth d at the current position and its position overlaps with the position of the current part to be printed. This invention can perform coarse-fine modulation in microseconds during the printing process, and can arbitrarily change the linewidth size according to the printing pattern when scanning the same line, thus improving printing efficiency.

Description

Technical Field

[0001] This invention belongs to the field of 3D printing technology, specifically relating to a printing method with dual laser modulation of linewidth. Background Technology

[0002] The purpose of SLM metal 3D printers is to manufacture parts by melting metal powder under the heat of a laser beam, cooling and solidifying it, and then stacking it into layers. SLM metal 3D printing has high requirements for the printing laser. It requires a pure single-mode output laser beam with a beam quality M2 of less than 1.1. Lasers with high beam quality usually have low laser power, which cannot be used to further improve printing efficiency. In addition, metal particle splatter in metal 3D printing can also seriously affect the printing quality. These are all common process problems in 3D printing.

[0003] Powder bed laser melting (PBLM) focuses a high-energy fiber laser beam into a small spot with sufficient energy to completely melt a thin layer of metal powder. A pair of scanning mirrors moves the laser across a powder bed, melting the metal powder and allowing it to solidify and connect with the underlying and adjacent layers, forming a molten pool. A protective gas flow passes over a processing tray to protect the hot metal from oxidation and safely remove fumes. The width of the molten pool is larger than the laser spot (approximately 2 to 3 times the spot diameter) because the heat generated by the laser is conducted to the surrounding powder particles, melting them into the moving molten pool. Multiple melting tracks connect and overlap, forming a solid metal layer corresponding to the layering of the part. The melting tracks must be deep enough to partially remelt the underlying metal layer to form a fully dense solid structure. Powder bed laser melting 3D printing equipment builds parts layer by layer in this manner.

[0004] According to the requirements of metal 3D printing technology, the laser power P and scanning speed V usually need to be properly matched, such as... Figure 1 As shown, if the scanning speed is too fast and the laser power is too low, some areas of the part may not melt completely, resulting in porosity due to "insufficient melting." Conversely, if the power applied at the selected speed is too high, the molten pool may overheat, causing the energy to penetrate too deeply, resulting in a "deep hole" effect. Between these two extremes lies an "operating window" within which a good part density can be obtained. Within this window, the laser energy is sufficient to completely melt the powder and the underlying metal layer without penetrating too deeply. It can be seen that simultaneously increasing laser power and scanning speed can improve processing efficiency, which is feasible to some extent. However, both power and speed have limits; once these limits are exceeded, the molten pool becomes unstable and a "spheroidizing" effect occurs. Figure 2As shown, as laser power increases, spatter may also increase, and when the scanning speed is too fast, the molten pool becomes unstable. A high surface tension gradient causes voids to form behind the laser beam. These voids expand as the laser moves, leading to the decomposition of the molten pool and eventual solidification into multiple unconnected spheres.

[0005] Therefore, in metal 3D printing, the aforementioned process characteristics limit the ability to improve part printing efficiency by increasing scanning speed. To improve printing efficiency, larger spot sizes and thicker scanning lines are typically used to print the infill parts of the part, while finer spot sizes are used to print the outlining lines. Patents "CN8799127U" and "CN5867306U" respectively present solutions using dual laser beams and optical zoom systems to scan the infill and outlining areas with thick and fine lines respectively. In these solutions, only one thickness can be selected when printing any scanning line. Due to the complex structure of the pattern, it is impossible to print the detailed structure of the pattern using traditional fixed-thickness scanning lines. To print the fine structure of the pattern, very fine laser beam lines are needed to scan many times, which further reduces printing efficiency. Therefore, traditional printing methods cannot simultaneously achieve both printing efficiency and printing accuracy. Summary of the Invention

[0006] The purpose of this invention is to provide a printing method with dual laser modulation linewidth to solve the problem that traditional 3D printing methods cannot simultaneously achieve both printing efficiency and printing accuracy.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows: This invention relates to a printing method for dual-laser modulated linewidths, which includes the following steps: S1. Set up two sets of elongated laser beams, both with a scanning width of D; S2. Divide the pattern to be printed into several printing blocks, the width of which shall not exceed D; S3. When printing the scan lines in each printing block, the power of both sets of long strip laser beams is modulated to be less than the power P required to melt the metal, and the sum of the power of the two sets of long strip laser beams is equal to the power required to melt the metal. The two sets of long strip laser beams scan synchronously along the length direction of the printing block. During the scanning process, the overlapping area of ​​the two sets of long strip laser beams is adjusted according to the actual line width d at the current printing position, so that the width of the overlapping area is the same as the actual line width d at the current position and the position overlaps with the position of the current part to be printed.

[0008] Preferably, the power of both sets of elongated laser beams in S3 is modulated to half of the power P required to melt the metal.

[0009] Preferably, during the S3 scanning process, the overlapping area of ​​the two sets of elongated laser beams is adjusted according to the actual line width d at the current printing position, so that the width of the overlapping area is the same as the actual line width d at the current position and the position overlaps with the position of the part to be printed. The specific method is as follows: the left edge of the scan line is used as the printing path of the left-hand elongated laser beam, and the width of the part of the left-hand elongated laser beam located on the right side of the corresponding printing path is the same as the actual line width d; the right edge of the scan line is used as the printing path of the right-hand elongated laser beam, and the width of the part of the right-hand elongated laser beam located on the left side of the corresponding printing path is the same as the actual line width d; and the parts of the two sets of elongated laser beams located between the left and right printing paths overlap, so that the sum of the power of the overlapping part is P.

[0010] Preferably, when S2 divides the pattern to be printed into several printing blocks, the width of each printing block is the same as the scanning width D of the elongated laser beam.

[0011] Preferably, step S3 further determines the scanning lines in the printing block. If the line width of the scanning lines at each position along the length direction is the same as the scanning width D of the long strip laser beam, proceed to step S4; otherwise, print according to step S3. S4. Adjust the power of one of the long strip laser beams to the power P required to melt the metal, and use a single long strip laser beam to print the scanned line.

[0012] Preferably, in step S4, when the scan line in one of the printing blocks is determined to have a line width at each position that is the same as the scanning width D of the long strip laser beam, it is determined whether there are still scan lines in the unprinted blocks that satisfy the condition that the line width at each position is the same as the scanning width D of the long strip laser beam. If so, the power of both sets of long strip laser beams is adjusted to the power P required to melt the metal, and the two sets of long strip laser beams are used to print the two printing blocks simultaneously.

[0013] Preferably, in step S1, the two sets of elongated laser beams are modulated by an acousto-optic modulator. Specifically, the laser beams are injected into the acousto-optic modulator, and signals of two ultrasonic frequencies are simultaneously input to the modulator to form first-order and second-order diffracted beams. The frequencies of the two ultrasonic waves are modulated, causing the first-order and second-order diffracted beams to deflect, with the deflection speed satisfying the following conditions: v 2 / v 1≥D / d', where, v 2 represents the deflection velocity of the first-order and second-order diffracted light. v 1 represents the scanning speed of the galvanometer unit, d' is the spot diameter, and the offset direction is perpendicular to the scanning direction of the galvanometer, thus forming two sets of long strip laser beams; The S3 controls the overlapping area of ​​the two sets of elongated laser beams by controlling the range of the ultrasonic frequency input to the acousto-optic modulator.

[0014] The two sets of elongated laser beams in S1 are obtained by splitting one incident laser beam into two beams through a laser beam splitting mechanism. The laser beam splitting mechanism includes a concave lens group, a beam splitter prism, and a convex lens group arranged sequentially along the laser beam path, and the concave lens group, beam splitter prism, and convex lens group are coaxially arranged. The method by which S1 forms two sets of elongated laser beams, each with a scanning width of D, is as follows: S1.1. An incident laser beam with a diameter of d0 is directed into a concave lens group, which is used to diffuse the incident laser beam. S1.2. By adjusting the distance between the concave lens group and the beam splitter, the diameter of the incident laser entering the beam splitter is 2D, and the beam splitter splits the incident laser into two groups of long strip lasers with a width of D. S1.3. Two sets of elongated laser beams are refracted by concave lenses to form two sets of elongated laser beams with a scanning width of D; S3 modulates the overlapping area of ​​the two sets of elongated laser beams by adjusting the spacing between the beam splitter prism and the convex lens group.

[0015] Compared with the prior art, the technical solution provided by this invention has the following advantages: 1. The dual-laser modulated linewidth printing method of the present invention sets up two sets of elongated laser beams to divide the pattern to be printed into several printing blocks. When printing the scanning lines in each printing block, the power of both sets of elongated laser beams is modulated to be less than the power P required to melt the metal, and the sum of the power of the two sets of elongated laser beams is equal to the power required to melt the metal. The two sets of elongated laser beams scan synchronously along the length direction of the printing block. During the scanning process, according to the actual linewidth d at the current printing position, the overlapping area of ​​the lasers of the two sets of elongated laser beams is adjusted so that the width of the overlapping area is the same as the actual linewidth d at the current position and the position overlaps with the position of the current part to be printed. The linewidth of the scanned printing is not constant and can be modulated in microseconds during the printing process. When scanning the same line, the size of the linewidth can be arbitrarily changed according to the printing pattern.

[0016] 2. The dual-laser modulated linewidth printing method of the present invention first determines the scanning lines in the printing block before printing the printing block. If the linewidth of the scanning line at each position in the length direction is the same as the scanning width D of a single long strip laser beam, then the power of one set of long strip laser beams can be adjusted to the power P required to melt the metal, and the scanning line can be printed using a single long strip laser beam. For multiple such printing blocks, the two sets of long strip laser beams can be printed simultaneously, taking into account printing efficiency. Attached Figure Description

[0017] Figure 1 This is a graph showing the relationship between laser power and scanning speed during SLM metal 3D printing. Figure 2 is a schematic diagram of the phenomenon that the molten pool becomes unstable due to excessive scanning speed; Figure 3 shows the division of the pattern to be printed into several printing blocks; Figure 4 is a schematic diagram of the principle of two sets of long strip laser beams jointly printing the scan lines in the printing block; Figure 5 A schematic diagram illustrating the determination of the laser overlap region for two sets of elongated laser beams; Figure 6 This is a schematic diagram illustrating the optimized printing method for the entire printed pattern; Figure 7 This is a schematic diagram illustrating the principle of using an acousto-optic modulator to modulate a long strip of light in Example 3. Figure 8 This is a structural diagram of the laser beam splitting mechanism used in Example 4; Figure 9 This is a schematic diagram illustrating the principle of the laser beam splitting mechanism used in Example 4 to modulate two sets of elongated light spots. Detailed Implementation

[0018] To further understand the content of this invention, the invention will be described in detail with reference to the embodiments. The following embodiments are used to illustrate the invention, but are not intended to limit the scope of the invention.

[0019] Example 1: This invention relates to a printing method for dual-laser modulated linewidths, which includes the following steps: S1. Set up two sets of elongated laser beams. The two sets of elongated laser beams are generated by two galvanometer modules respectively. The scanning width of the two sets of elongated laser beams is D. That is, the scanning laser spot generated by the two sets of galvanometer modules is an elongated spot with a length of D. The elongated spot can be formed by combining several circular spots arranged in a straight line and tangent to each other.

[0020] S2. See Appendix Figure 3 As shown, the pattern to be printed is divided into several printing blocks. The width of each printing block is no greater than D. To facilitate the division and subsequent steps, the width of the printing area is generally uniform. It can be seen that the width of the laser scanning lines in each printing area is often uneven. S3. When printing the scan lines in each printing block, the power of both sets of elongated laser beams is modulated to be less than the power P required to melt the metal, and the sum of the powers of the two sets of elongated laser beams is equal to the power required to melt the metal. Generally, the power of both sets of elongated laser beams is modulated to half of the power P required to melt the metal, i.e., P / 2. The two sets of elongated laser beams scan synchronously along the length of the printing block, and during the scanning process, the overlapping area of ​​the two sets of elongated laser beams is adjusted according to the actual line width d at the current printing position, so that the width of the overlapping area is the same as the actual line width d at the current position and the position overlaps with the position of the current part to be printed. Figure 5 As shown, the specific method is as follows: the left edge of the scanned line is used as the printing path for the left-hand elongated laser beam. The width of the portion of the left-hand elongated laser beam (laser beam 1) located on the right side of the corresponding printing path is the same as the actual line width d. The right edge of the scanned line is used as the printing path for the right-hand elongated laser beam. The width of the portion of the right-hand elongated laser beam (laser beam 2) located on the left side of the corresponding printing path is the same as the actual line width d. The two sets of elongated laser beams overlap between the left and right printing paths, so that the sum of the power of the overlapping portion is P. When the two sets of elongated laser beams scan at the same scanning speed and continuously adjust the overlapping area, the area of ​​the scanned line is printed. Its working principle is as follows. Figure 4 As shown, each set of elongated laser beams (laser beam 1 and laser beam 2) has a power of 50% of the power required for the printing process. The beams from the two galvanometers are combined, and the superimposed energy is the laser energy required for the printing process. The scanning lines of the two galvanometers overlap in a certain proportion. Since the power of each laser beam is only 50% of the power required for printing, only the overlapping part of the two laser beams has enough laser energy to print and sinter the metal powder. Before the metal powder is heated to its melting point, it exists in a solid powder state. The energy in the non-overlapping part of the two beams is insufficient to reach the state of the metal powder. After laser scanning, the state is the same as before printing. At this time, the equivalent linewidth of the scanned print is the overlapping part of the two laser beams.

[0021] Example 2: This embodiment is a further improvement on embodiment 1, and the specific steps are as follows: S1. Set up two sets of elongated laser beams. The two sets of elongated laser beams are generated by two galvanometer modules respectively. The scanning width of the two sets of elongated laser beams is D. That is, the scanning laser spot generated by the two sets of galvanometer modules is an elongated spot with a length of D. The elongated spot can be formed by combining several circular spots arranged in a straight line and tangent to each other.

[0022] S2. See Appendix Figure 3 As shown, the pattern to be printed is divided into several printing blocks. In this embodiment, the width of each printing block is the same as the scanning width D of the long strip laser beam. S3. Before printing the scan lines in each printing block, the scan lines in the printing block are first judged. If the line width of the scan line at each position in the length direction is the same as the scanning width D of the long strip laser beam, then skip the subsequent steps of S3 and proceed directly to S4. Otherwise, the power of the two sets of long strip laser beams is modulated to be less than the power P required to melt the metal, and the sum of the power of the two sets of long strip laser beams is equal to the power required to melt the metal. Generally, the power of the two sets of long strip laser beams is modulated to half of the power P required to melt the metal, i.e., P / 2. The two sets of long strip laser beams scan synchronously along the length direction of the printing block. During the scanning process, according to the actual line width d at the current printing position, the overlapping area of ​​the lasers of the two sets of long strip laser beams is adjusted so that the width of the overlapping area is the same as the actual line width d at the current position and the position overlaps with the position of the current part to be printed. The specific implementation method and working principle are the same as in Example 1, and will not be described in detail in this example.

[0023] S4. Further determine whether there are any scan lines in the unprinted area that satisfy the condition that the line width at each position is the same as the scanning width D of the long strip laser beam. If so, adjust the power of both sets of long strip laser beams to the power P required to melt the metal, and use both sets of long strip laser beams to print the two printed areas simultaneously. If not, adjust the power of one set of long strip laser beams to the power P required to melt the metal, and use a single long strip laser beam to print the scan line. Figure 6 As shown. This embodiment is more suitable for scenarios where the printed pattern is relatively regular. The reason is that when the printed pattern is relatively regular, there are a large number of scanning line widths in the middle of the printed pattern that are the same as the scanning width D of a single long strip laser beam. Therefore, step S3 is used to print the scanning lines in the printing blocks at the edge of the printed pattern, and step S4 is used to print the printing area where the scanning line width is the same as the scanning width D of a single long strip laser beam. In this way, the printing efficiency can be improved.

[0024] Example 3 Examples 1 and 2 require two sets of galvanometer systems to generate two sets of elongated laser beams. This example is a further improvement on Examples 1 and 2. Specifically, this example no longer uses two sets of galvanometer systems; instead, the two sets of elongated laser beams are modulated by a single acousto-optic modulator. Specifically: S1. A laser beam is injected into an acousto-optic modulator. Two ultrasonic frequency signals are simultaneously input into the acousto-optic modulator, forming first-order and second-order diffracted beams. The frequencies of the two ultrasonic waves are modulated, causing the first-order and second-order diffracted beams to deflect. The deflection velocities satisfy... v 2 / v 1≥D / d', where, v1 represents the scanning speed of the galvanometer unit, d' is the spot diameter, and the offset direction is perpendicular to the scanning direction of the galvanometer, thus forming two sets of long strip laser beams; S2. Divide the pattern to be printed into several printing blocks. In this embodiment, the width of each printing block is the same as the scanning width D of the long strip laser beam. S3. By controlling the range of the ultrasonic frequency input to the acousto-optic modulator, the overlapping area of ​​the two sets of elongated laser beams can be controlled.

[0025] Example 4 Examples 1 and 2 require two sets of galvanometer systems to generate two sets of elongated laser beams. This example is a further improvement on Examples 1 and 2. Specifically, this example no longer uses two sets of galvanometer systems, but instead uses a laser beam splitting mechanism to split one incident laser beam into two beams to obtain two sets of elongated laser beams; see attached... Figure 8 As shown, a laser beam splitting mechanism is installed in front of the XY-axis galvanometer of the original scanning system. The laser beam splitting mechanism includes a concave lens group, a beam splitter prism, and a convex lens group arranged sequentially along the laser beam path. The concave lens group, beam splitter prism, and convex lens group are coaxially arranged. It should be noted that... Figure 8 The XY-axis galvanometer and FTheta field mirror are commonly used components in laser scanning systems and are existing technologies. This embodiment adds a laser beam splitting mechanism to the existing scanning system, and the original scanning system will not be explained in detail.

[0026] See attached document Figure 9 As shown, the method by which S1 forms two sets of elongated laser beams, each with a scanning width of D, is as follows: S1.1. An incident laser beam with a diameter of d0 is directed into a concave lens group, which is used to diffuse the incident laser beam. S1.2. By adjusting the distance between the concave lens group and the beam splitter, the diameter of the incident laser entering the beam splitter is 2D, and the beam splitter splits the incident laser into two groups of long strip lasers with a width of D. S1.3. Two sets of elongated laser beams are refracted by concave lenses to form two sets of elongated laser beams with a scanning width of D. Assume that the refractive index of the beam splitter prism is... n , No. i The inclination angle of each exit surface is θ i The deflection angle of the emitted beam is α i ,but α i The calculation formula is as follows: ; Therefore, the deflection angle α iThe refractive index of the beam splitter material is related to the tilt angle of the exit surface. When a beam splitter is provided, the deflection angle... α i It is constant and unchanging; Furthermore, since the width of the incident laser is 2D when it is incident on the beam splitter, and the beam splitter is coaxial with the concave lens, after the beam is split, the width of the two laser beams is D, and the power of the two laser beams after the beam is split is P / 2. S2. Divide the pattern to be printed into several printing blocks; S3. The overlap area of ​​the two sets of elongated laser beams is modulated by adjusting the spacing between the beam splitter prism and the convex lens group, such as... Figure 9 As shown, according to the imaging principle of a convex lens group, the angle between the two laser beams after beam splitting is... β It can be expressed by the following formula: , Wherein, the initial diameter of the incident laser d 0 The value is determined based on the incident laser and is constant within the system. In step S1, to ensure that the width of the elongated laser beam after splitting is D, the distance between the concave lens group and the beam splitter prism has been adjusted. L 1 The deflection angle of the laser beam emitted from the exit surface of the beam splitter. α It is also constant, so only the distance between the beam splitter and the convex lens group needs to be adjusted. L 2 This allows you to adjust the angle between the two split laser beams. β This allows for the adjustment of the overlapping area of ​​the two long, strip-shaped laser beams.

[0027] The present invention has been described in detail above with reference to the embodiments, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made in accordance with the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A printing method with dual laser-modulated linewidths, characterized in that, It includes the following steps: S1. Two sets of elongated laser beams are set up, each with a scanning width of D. The two sets of elongated laser beams are modulated by an acousto-optic modulator. Specifically, the laser beams are injected into the acousto-optic modulator, and two ultrasonic frequency signals are simultaneously input to the acousto-optic modulator to form first-order diffracted light and second-order diffracted light. The frequencies of the two ultrasonic waves are modulated, causing the first-order and second-order diffracted light to deflect. The deflection speed satisfies v2 / v1≥D / d', where v2 represents the deflection speed of the first-order and second-order diffracted light, v1 represents the scanning speed of the galvanometer unit, d' is the spot diameter, and the deflection direction is perpendicular to the scanning direction of the galvanometer, thus forming two sets of elongated laser beams. S2. Divide the pattern to be printed into several printing blocks, the width of which shall not exceed D; S3. When printing the scan lines in each printing block, the power of both sets of elongated laser beams is modulated to be less than the power P required to melt the metal, and the sum of the power of the two sets of elongated laser beams is equal to the power required to melt the metal. The two sets of elongated laser beams scan synchronously along the length of the printing block. During the scanning process, based on the actual line width d at the current printing position, the range of the ultrasonic frequency input to the acousto-optic modulator is controlled to control the overlapping area of ​​the two sets of elongated laser beams, so that the width of the overlapping area is the same as the actual line width d at the current position and the position overlaps with the position of the current part to be printed. Specifically, the left edge of the scan line is used as the printing path of the left-hand elongated laser beam, and the width of the part of the left-hand elongated laser beam on the right side of the corresponding printing path is the same as the actual line width d; the right edge of the scan line is used as the printing path of the right-hand elongated laser beam, and the width of the part of the right-hand elongated laser beam on the left side of the corresponding printing path is the same as the actual line width d; and the parts of the two sets of elongated laser beams between the left and right printing paths overlap, so that the sum of the power of the overlapping part is P.

2. The printing method for dual-laser modulated linewidth according to claim 1, characterized in that: In S3, the power of both sets of elongated laser beams is modulated to half of the power P required to melt the metal.

3. The printing method for dual-laser modulated linewidth according to claim 1, characterized in that: When S2 divides the pattern to be printed into several printing blocks, the width of each printing block is the same as the scanning width D of the elongated laser beam.

4. The printing method for dual-laser modulated linewidth according to claim 3, characterized in that: S3 further determines the scanning lines in the printing block. If the line width of the scanning lines at each position in the length direction is the same as the scanning width D of the long strip laser beam, proceed to S4; otherwise, print according to the method of S3. S4. Adjust the power of one of the long strip laser beams to the power P required to melt the metal, and use a single long strip laser beam to print the scanned line.

5. The printing method for dual-laser modulated linewidth according to claim 4, characterized in that: In step S4, when the scan line in one of the printing blocks is determined to have a line width at each position that is the same as the scanning width D of the long strip laser beam, it is determined whether there are still scan lines in the unprinted blocks that satisfy the condition that the line width at each position is the same as the scanning width D of the long strip laser beam. If so, the power of both sets of long strip laser beams is adjusted to the power P required to melt the metal, and the two sets of long strip laser beams are used to print the two printing blocks simultaneously.

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