A scanning laser printhead

Abstract

This invention relates to a printhead for 3D printing, particularly a printhead based on scanning laser heating, belonging to the field of additive manufacturing technology. Compared with existing coaxial filament feeding laser cladding heads / printheads, this invention offers significant advantages, such as: enabling flexible heating strategies; supporting the printing of finer structures; avoiding overheating of freshly deposited material; providing extremely high tolerance for mechanical assembly precision between the laser path's mechanical structure and other parts of the printhead; creating a stirring effect on the molten pool, improving the performance of the final 3D printed part; preheating the area where material will be deposited, reducing the temperature gradient between the molten pool area and other areas of the workpiece, thereby suppressing thermal cracking; and integrating laser cleaning during the 3D printing process, enabling 3D printing in air without the use of protective gases, resulting in lower costs. This invention represents a significant and substantial advancement.

Description

Technical Field

[0001] This invention relates to a printhead for 3D printing, and more particularly to a printhead based on scanning laser heating, belonging to the field of additive manufacturing technology. Background Technology

[0002] 3D printing, also known as additive manufacturing, is a major category of advanced manufacturing technologies. 3D printing uses various forms of raw materials, such as liquids, solid powders, granules, filaments, rods, and wires. Among these, filaments are often cheaper, easier to store, safer, and more environmentally friendly than powders. Existing 3D printing technologies that use lasers as a heating source and filaments as raw materials include two types: "off-axis filament feeding" and "coaxial filament feeding." For example, the technical solution disclosed in Chinese patent application number 2018800071130 adopts a "side-axis wire feeding" method. In this technology, the laser beam is perpendicular to the current forming surface, and the filament is transported from outside the space enclosed by the laser beam to the surface of the workpiece (also known as the printed body, which is an object formed after the molten raw material is deposited). The laser beam melts the filament and the area of ​​the workpiece surface adjacent to the filament together. This method does not need to consider the problem of the filament blocking the laser, and the optical path structure is relatively simple. However, it has problems such as directional defects in printing, difficulty in printing path planning, complex programming of multi-axis motion platforms, low surface quality of parts, low printing efficiency, and difficulty in printing complex structures. The paper entitled "A Comprehensive Study of Auxiliary Arrangements for Attaining Omnidirectionality in Additive Manufacturing Machine Tools" (DOI:10.1115 / 1.4049094) discusses the directional problems faced by "side-axis wire feeding" in additive manufacturing. In order to solve the problems of the wire blocking the laser beam and being heated and melted too early, the "coaxial wire feeding method" generally expands the laser beam first, then shapes it into a ring laser beam (hollow laser beam), the wire passes through the center of the ring laser beam, and then the ring laser beam is focused, and the wire melts near the focal point of the laser beam. For example, the technical solutions disclosed in Chinese patent applications with application numbers 2018103767579 and 2018104031543 adopt a "coaxial wire feeding" method. There is no laser in the axial space of the laser beam (i.e., the center of the laser beam). The wire is transported to the surface of the workpiece along the center of the laser beam. The laser beam is focused on the surface of the workpiece and melts the wire and the area of ​​the workpiece surface adjacent to the wire. The optical path of this method is more complex and the optical path is more difficult to manufacture than that of the off-axis wire feeding method. However, since the wire is perpendicular to the surface of the workpiece where the molten material is accumulating (also known as depositing), the wire and the laser beam can print together on the surface of the workpiece in any direction. This solves the directional problem caused by the traditional off-axis wire feeding method. It also has many advantages that are not easy to obtain by off-axis wire feeding, such as simple printing path planning, simple required motion platform structure, simple program programming, higher part surface quality, and the ability to print complex structures. Summary of the Invention

[0003] The inventors discovered that in existing coaxial filament feeding methods, the positional relationship between the laser beam and the filament, as well as the relative positional relationship between the laser spot and the filament or the molten material generated by the filament, is relatively fixed. This results in a lack of printing flexibility. Specifically, for example, in the metal 3D printing process, the metal filament is heated and melted and deposited on the workpiece. Immediately after the molten metal is deposited, it is heated by the annular laser spot projected onto the workpiece surface. The deposited molten metal is overheated, leading to increased fluidity. This increased fluidity further results in problems such as low shape controllability, rough surface morphology, and low forming accuracy. Overheating also leads to increased evaporation and increased porosity. To avoid heating the newly deposited molten metal, the laser beam needs to be able to quickly adjust the position of the laser spot around the molten metal according to changes in the printing path. However, existing laser coaxial filament feeding 3D printing technology does not possess this flexibility. For example, in the metal 3D printing process, the annular spot of the laser beam projected onto the workpiece and surrounding the molten metal also heats areas not on the printing path, resulting in a large molten pool and a large heat-affected zone. When printing delicate structures such as thin-walled structures with slow heat dissipation, this can lead to overheating, damage, or deformation. An ideal heating method would be to heat the area in front of the printing path, with the width of the molten pool roughly matching the width of the thin-walled structure. This requires the laser beam to be able to quickly adjust the spot position according to changes in the printing path, a flexibility that existing coaxial laser wire-feeding 3D printing technology lacks. These existing problems stem from the limitations of the annular spot laser head used in coaxial laser wire-feeding 3D printing technology. Annular spot laser heads can also be applied to laser welding systems, but they also suffer from the same limitations. Furthermore, since the existing laser "coaxial wire feeding" heating method is the same as the "heat conduction method" of laser welding, the laser spot power density is the same as that of traditional heat conduction laser welding. The spot power density value cannot cause significant vaporization of the heated workpiece or raw material, otherwise it will seriously harm the 3D printing process. Therefore, it is impossible to achieve the "laser cleaning" function by increasing the spot power density.

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide a laser printhead (also known as a laser cladding head) that uses one or more laser beams to heat the printhead by scanning, which can flexibly perform scanning laser heating, and is different from the existing "coaxial wire feeding" laser cladding head / printhead.

[0005] To achieve the aforementioned objectives, the technical solution adopted by this invention is as follows:

[0006] A scanning laser printhead, characterized in that:

[0007] The system is equipped with a laser interface, a beam-shifting focusing lens group, and a material delivery channel. The laser beam from the laser interface is modulated by the beam-shifting focusing lens group and then projected onto the workpiece from the space surrounding the material delivery channel. The printing material, which can be liquid or solid, arrives at the workpiece via the material delivery channel. The molten material, formed by melting the liquid or solid material, is deposited on the workpiece. (Explanation: The workpiece is the object formed after the printing material is deposited during the 3D printing process.)

[0008] The aforementioned beam-shifting focusing lens assembly can be rotated and / or moved to modulate the position of the laser beam projected onto the workpiece, thereby enabling the laser beam to scan and heat the edges and / or periphery of the area on the workpiece where material is being deposited; while scanning and heating the edges and / or periphery of the area on the workpiece where material is being deposited, the scanning and heating area of ​​the laser beam on the workpiece also moves relative to the workpiece; (Explanation: In the 3D printing process, the print head moves relative to the workpiece, and the scanning and heating area of ​​the laser beam on the workpiece also moves relative to the workpiece;)

[0009] The number of projectable laser beams is at least two; each laser beam can be independently controlled; the number of laser beams projected at the same time is controllable; correspondingly, the number of laser interfaces and beam-moving focusing lens groups is the same as the number of laser beams, and each laser beam corresponds to one laser interface and one beam-moving focusing lens group.

[0010] The area where the raw material is being deposited refers to the area on the workpiece that is in contact with the raw material being deposited;

[0011] The edge of the area where the raw material is being deposited refers to the edge of the area on the workpiece that is in contact with the raw material being deposited.

[0012] The periphery of the area where the raw material is being deposited refers to the area on the workpiece that is adjacent to or connected to the area where the raw material is being deposited.

[0013] (Explanation: "Raw material being deposited" refers to raw material that has already come into contact with the workpiece and is located in the space between the outlet of the raw material conveying channel and the workpiece.)

[0014] Optional:

[0015] The aforementioned beam-shifting focusing lens assembly includes a beam-shifting lens and a focusing lens, which are independent components. By rotating and / or moving the beam-shifting lens, the position of the laser beam projected onto the workpiece is modulated, thereby enabling the laser beam to scan and heat the edge and / or periphery of the area on the workpiece where the raw material is being deposited. The focusing lens is used to focus the laser beam. (It should be noted that the "beam-shifting lens" here refers to a lens that can change the position of the beam projection, and does not necessarily have the function of focusing the beam.)

[0016] Optional:

[0017] The aforementioned beam-moving lens can be translated or rotated in one dimension to enable one-dimensional movement of the laser beam (also known as one-dimensional scanning); or, the beam-moving lens can be translated or rotated in two dimensions to enable two-dimensional movement of the laser beam (also known as two-dimensional scanning). When the laser beam moves in two dimensions, and the focusing lens is electrically and programmably focused, two-dimensional scanning in the X and Y axes is performed by the beam-moving lens, and scanning in the Z axis is performed by focusing the focusing lens, thereby enabling the focal point of the laser beam to be scanned in three-dimensional space (also known as three-dimensional scanning).

[0018] Optional:

[0019] The aforementioned beam-moving focusing lens group comprises at least one rotatable and / or movable focusing lens, which is used to move and focus the laser beam. By rotating and / or moving the focusing lens, the position of the laser beam projected onto the workpiece is modulated, thereby enabling the laser beam to scan and heat the edge and / or periphery of the area on the workpiece where the raw material is being deposited.

[0020] Optional:

[0021] The focusing lens can be translated or rotated in one dimension to move the laser beam in one dimension (also known as one-dimensional scanning); or, the focusing lens can be translated or rotated in two dimensions to move the laser beam in two dimensions (also known as two-dimensional scanning); or, the focusing lens can be translated or rotated in two dimensions to move the laser beam in one dimension and focus the focusing lens; or, the focusing lens can be translated or rotated in three dimensions to move the laser beam in two dimensions and focus the focusing lens (in this case, when the focusing lens can be electrically focused and programmably focused, it can scan in the X and Y axis directions through the focusing lens, and also scan in the Z axis direction through focusing the focusing lens, thereby realizing the scanning of the focal point of the laser beam in three-dimensional space), thus changing both the planar scanning position of the light spot on the workpiece surface and the area of ​​the light spot on the workpiece surface.

[0022] Optional:

[0023] The aforementioned beam-shifting focusing lens group includes two sets of lenses, which are sequentially arranged on the propagation path of the laser beam. The two sets of focusing lenses rotate around their respective axes of rotation, and the axes of rotation of the two sets of lenses are perpendicular to each other (for example, one set of lenses is a concave lens (diverging light) and the other set is a convex lens (converging light)).

[0024] Optional:

[0025] Each lens group includes at least one lens, which is either a convex or concave lens, and at least one of the two lens groups is a convex lens as a focusing lens.

[0026] Optional:

[0027] When the raw material is solid, the laser beam also heats the solid raw material outside the outlet of the raw material conveying channel to generate molten raw material in the space between the outlet of the raw material conveying channel and the workpiece.

[0028] Optional:

[0029] When two or more laser beams are simultaneously projected onto a workpiece, the laser beam spot scanning area projected onto the workpiece can form a composite scanning area, which can surround the area on the workpiece where the raw material is being deposited.

[0030] Optional:

[0031] The laser beam scans and heats the edge and / or periphery of the area on the workpiece where the raw material is being deposited, to generate a molten pool;

[0032] When the number of projected laser beams is two or more, the power of each laser beam can be controlled independently;

[0033] When the number of projected laser beams is two or more, the scanning parameters of each laser beam can be controlled independently.

[0034] Optional:

[0035] The focusing lens mentioned is either a field lens or a non-field lens; (Here, a field lens, also called a flat field lens or f-theta lens, is a specialized lens system whose function is to form a uniformly sized focused spot of the laser beam across the entire marking plane, and is one of the most important components of a laser marking machine.)

[0036] The beam-moving lens or focusing lens is driven by electromagnetic force (e.g., electric motor drive, electromagnet drive), or by piezoelectric element (e.g., piezoelectric ceramic drive), or by thermo-deformation drive (e.g., a drive mechanism using thermo-deformation material as the drive component), or by magneto-deformation drive (e.g., a drive mechanism using magneto-deformation material as the drive component), or by electro-deformation drive (e.g., a drive mechanism using electro-deformation material as the drive component), or by fluid drive (e.g., cylinder drive, hydraulic push rod drive, etc.).

[0037] Optional:

[0038] The beam-moving lens is located either before or after the focusing lens in the propagation path of the laser beam.

[0039] Optional:

[0040] A collimating lens is provided to convert a non-parallel laser beam into a parallel laser beam. The collimating lens is located before the laser interface in the propagation path of the laser beam.

[0041] A beam splitter is provided to split a laser beam into at least two beams, and the beam splitter is located before the laser interface in the propagation path of the laser beams.

[0042] A window mirror is provided to prevent external substances from contacting the light beam moving focusing lens group;

[0043] A gas passage is provided for spraying gas to form a gas curtain, through which the gas curtain prevents or reduces the contamination of the beam moving focusing lens group and the window mirror by external substances, and / or for spraying protective gas onto the molten pool on the raw material and workpiece being deposited to form a protective atmosphere (e.g., spraying argon gas into the space where the raw material and molten pool are being deposited to form an inert gas protective atmosphere).

[0044] A liquid cooling channel is provided for cooling the scanning laser printhead;

[0045] It is equipped with an optical path switching component to switch the laser beam from one laser interface to another.

[0046] Optional:

[0047] It also includes housings of the same number as the laser beam, with both ends of the housings being open, the upper opening of the housing forming the laser interface, and the lower opening of the housing forming the laser emission port. The beam moving focusing lens group is disposed inside the housing, and the housing is connected to the raw material conveying channel.

[0048] Optional:

[0049] The focusing lens is adjustable, and the focusing method can be manual focusing, electric focusing, pneumatic focusing, or hydraulic focusing.

[0050] Optional:

[0051] The laser interface is connected to the laser output head of the laser.

[0052] Optional:

[0053] The area on the workpiece that is to be heated by the laser beam along the raw material deposition path can be preheated before it is heated by the laser beam to form a molten pool, and the range of preheating can be set. Here, "preheating" can reduce the temperature gradient between the area where raw material is being deposited and other areas of the workpiece, thereby suppressing the generation of hot cracks and reducing stress.

[0054] Optional:

[0055] The aforementioned beam-shifting focusing lens group controls the laser beam to heat the edge of the material being deposited, thereby conducting heat through the material to the edge of the area where the material is being deposited on the printed body, thus indirectly scanning and heating the edge of the area where the material is being deposited on the printed body. (Explanation: When the area where the material is being deposited is in contact with the material being deposited, causing that area to be covered by the material, the laser beam cannot directly heat the area on the workpiece surface covered by the material. It needs to heat the material being deposited, and then conduct heat through the material to the area where the material is being deposited. Because the edge of the material being deposited is thin and in close contact with the printed body, its heat is quickly conducted away by the printed body. Of course, if the laser beam directly heats the periphery of the area where the material is being deposited that is connected to or adjacent to the edge of the area where the material is being deposited, the heat from that periphery will also be transferred to the edge of the area where the material is being deposited through heat conduction, thus indirectly heating the edge of the area where the material is being deposited.)

[0056] Optional:

[0057] The number of projected laser beams is at least two. One part of the laser beam scans and heats the edge and / or periphery of the area on the workpiece where the raw material is being deposited to generate a molten pool. The other part of the laser beam trims the shape of the already printed workpiece surface (trimming includes cutting, engraving, cleaning, etc., to obtain better surface quality).

[0058] Optional:

[0059] The aforementioned beam-moving focusing lens group controls the laser beam to heat the material being deposited while simultaneously scanning and heating the edge and / or periphery of the area where the material is being deposited.

[0060] Optional:

[0061] The laser beam scans and heats the interface between the workpiece surface and the raw material being deposited, thereby performing laser cleaning on the interface.

[0062] The beneficial effects of this invention are as follows:

[0063] (1) Compared with the existing "coaxial wire feeding" laser cladding head (print head), the present invention can also obtain an annular spot to heat the edge and / or periphery of the area on the workpiece where the raw material is being deposited, but the present invention is more flexible.

[0064] (2) Compared with the existing "coaxial wire feeding" laser cladding head (print head), the present invention can achieve a flexible heating strategy by adjusting the scanning position of the laser beam spot during the three-dimensional printing process. For example, two lasers are used, one of which is responsible for heating the area of ​​the printed body (i.e. the workpiece) that is connected to or adjacent to the area where the raw material is being deposited in front of the printing path with high power, while the other laser only heats the surface of the printed body and the raw material that has just been deposited with low power to obtain a smoother surface and avoid serious problems (such as significant vaporization) caused by overheating due to high power heating of the raw material that has just been deposited; or, according to the characteristics of the surrounding structure of the area where the raw material is accumulating, the scanning strategy corresponding to the minimum stress is calculated, and the scanning range and scanning path of the spot are dynamically adjusted.

[0065] (3) Compared with the existing "coaxial wire feeding" laser cladding head (print head), the present invention reduces the thermal influence range of the laser by adopting a laser scanning heating strategy that only heats the area of ​​the printed body surface located in front of the printing path and adjacent or connected areas when printing thin-walled structures, thereby avoiding overheating of thin-walled structures and reducing deformation. The present invention has more advantages when printing thin-walled structures and is more suitable for printing complex and fine structures.

[0066] (4) Compared with the existing "coaxial wire feeding" laser cladding head (print head), the present invention can also irradiate and heat the area on the workpiece surface where the raw material is about to be deposited (accumulated) without heating the raw material that has just been deposited. This avoids overheating the raw material that has just been deposited (overheating will lead to higher fluidity or vaporization), and can obtain higher molding accuracy. The part material has fewer micropores and higher density, which is of greater significance for additive manufacturing applications. Therefore, the present invention can be used for higher precision additive manufacturing.

[0067] (5) Compared with the existing "coaxial wire feeding" laser cladding head (print head), the present invention adopts the rotation and / or movement control of the moving and focusing lens group to control the dynamic scanning of the laser. The projection position of the laser beam is dynamically adjustable, and it has extremely high fault tolerance for the mechanical assembly accuracy between the optical path mechanical structure and the raw material conveying channel and other components.

[0068] (6) Compared with the existing "coaxial wire feeding" laser cladding head (print head), the present invention uses laser scanning to generate a molten pool on the printed body (workpiece). The "scanning method" can produce a "stirring" effect on the molten pool, which has a beneficial effect on the performance of the parts finally obtained by 3D printing, such as reducing micropores.

[0069] (7) Compared with existing coaxial filament feeding laser cladding heads (print heads), this invention uses laser scanning to heat the printed body (workpiece), which can preheat the area where raw material will be deposited, reduce the temperature gradient between the area where raw material is being deposited and other areas of the printed body (workpiece), suppress the generation of thermal cracks, and improve the material properties of 3D printed parts (mainly mechanical properties, such as the fatigue resistance of metal parts). Existing metal 3D printing technologies, especially Selective Laser Melting (SLM) and Direct Energy Deposition (DED) (existing laser-heated coaxial and off-axis filament feeding 3D printing systems, arc-heated off-axis filament feeding 3D printing systems, and laser-heated coaxial powder feeding and off-axis powder feeding 3D printing systems all belong to DED technology), generally suffer from low fatigue resistance of parts, which is also a huge obstacle restricting the application of existing metal 3D printing technology in industrial production.

[0070] (8) Because the existing laser "coaxial wire feeding" heating method is the same as the "heat conduction method" of traditional laser welding (the existing laser coaxial wire feeding metal 3D printing is essentially laser welding), that is, the laser spot power density range is the same as that of traditional heat conduction laser welding. The spot power density value cannot cause significant vaporization of the heated workpiece or raw material, otherwise it will seriously harm the 3D printing process. Therefore, it is impossible to achieve the "laser cleaning" function by increasing the spot power density. However, the present invention uses a scanning heating method, which can quickly disperse heat over a larger area. It can diffuse heat without relying on the "heat conduction" method. Therefore, a higher power density laser beam can be used to simultaneously achieve "laser cleaning" while heating to generate a molten pool. This removes substances harmful to 3D forming (such as removing oxide films) from the molten pool and the surface of the raw material being deposited. Combined with resistance heating and other methods to generate molten raw material, it can counteract the toxic effects of air on the 3D forming process. Therefore, the present invention can achieve 3D printing in air without the use of protective gas, has lower costs, and can print metal components in open environments. Laser cleaning, also known as laser ablation or photoablation, is a process of removing material from a solid (or sometimes liquid) surface by irradiating it with a laser beam. The surface material is heated and evaporated or sublimated by the absorbed laser energy. Typically, laser cleaning refers to removing a thin layer of material from the surface of an object using a pulsed laser without damaging the underlying structure. In rare cases, continuous laser ablation can be used to remove a thin layer of material from the surface of an object, but due to the extremely high energy of continuous lasers, the thermal effect is very severe, for example, causing remelting of solid metal surfaces, i.e., creating a molten pool (thin molten pool) while ablating the metal. This invention utilizes the characteristic of continuous lasers to generate a molten pool when used as a heat source for laser cleaning.

[0071] In summary, compared with existing coaxial filament feeding laser cladding heads (print heads), the present invention offers the following advantages: it enables flexible heating strategies; it allows for the printing of finer structures; it avoids overheating of the raw material after deposition, resulting in fewer micropores and higher density within the part material; it has extremely high tolerance for mechanical assembly precision between the optical path and components such as the raw material delivery channel; it creates a stirring effect on the molten pool, improving the performance of the final 3D printed part; it can preheat the area where the raw material is about to be deposited, reducing the temperature gradient between the area where the raw material is being deposited and other areas of the workpiece (printed body), thus suppressing the generation of thermal cracks; it enables 3D printing in air without the use of protective gas, resulting in lower costs; and it allows for the printing of large metal components in open environments. This invention represents a significant and substantial advancement. Attached Figure Description

[0072] Figure 1This is a three-dimensional perspective view used to illustrate the composition of a first specific embodiment of a scanning laser printhead according to the present invention;

[0073] Figure 2 yes Figure 1 Front view;

[0074] Figure 3 yes Figure 1 The specific embodiment shown is in operation, in order to Figure 2 Front view perspective;

[0075] Figure 4 This is a schematic diagram for illustration. Figure 1 The structure of the specific embodiment shown;

[0076] Figure 5 This is a schematic diagram for illustration. Figure 1 The specific embodiment shown illustrates the positional relationship between the laser beam spot on the workpiece and the raw material;

[0077] Figure 6 This is a schematic diagram for illustration. Figure 1 The specific embodiment shown illustrates the scanning area of ​​the laser beam on the workpiece and its positional relationship with the raw material;

[0078] Figure 7 It is a three-dimensional perspective view used for illustration. Figure 1 The functional structure for moving the light beam used in the specific embodiment shown;

[0079] Figure 8 yes Figure 7 Top view;

[0080] Figure 9 It is a three-dimensional perspective view used to illustrate the functional structure for moving the light beam of a second specific embodiment of a scanning laser printhead of the present invention;

[0081] Figures 10 to 15 This is a schematic diagram illustrating the laser scanning strategy of the present invention.

[0082] The labels are:

[0083] 101-Housing 1, 102-Laser Interface 1, 103-Laser Interface 2, 104-Laser Interface 3, 105-Laser Interface 4, 106-Raw Material Conveying Channel, 107-Coolant Interface, 108-Gas Interface 1, 109-Gas Interface 2, 110-Cooling Chamber, 111-Gas Interface 4, 112-Linear Solid Raw Material, 113-Workpiece, 114-Laser Beam 1, 115-Laser Beam 2, 116-Laser Beam 3, 117-Laser Beam 4, 118-Translation Lens 2, 119-Focusing Lens 2, 120-Window Lens 2, 121-Translation Lens 4, 122-Focusing Lens 4, 123-Window Lens 4, 124-Scanning Range 1, 125-Scanning Range 2, 126-Scanning Range 3, 127-Scanning Range 4;

[0084] 128-Concave lens, 129-Outer shell, 130-Electromagnetic element one, 131-Permanent magnet one, 132-Spring one, 133-Electromagnetic element two, 134-Permanent magnet two, 135-Spring two, 136-Electromagnetic element three, 137-Permanent magnet three, 138-Spring three;

[0085] 139-Rotating lens one, 140-Rotating axis one, 141-Rotating lens two, 142-Rotating axis two, 143-Incident beam, 144-First-stage scanning beam, 145-Second-stage scanning beam;

[0086] 146 - Projection of linear solid material on the surface of the workpiece; 237 - Scanning pattern one; 238 - Scanning pattern two; 239 - Overlapping area; 240 - Scanning pattern three; 241 - Scanning pattern four; 242 - Scanning pattern five; 243 - Scanning pattern six; 244 - Scanning pattern seven; 245 - Scanning pattern eight; 246 - Scanning pattern nine; 247 - Scanning pattern ten.

[0087] Arrow D1 - Rotation direction one, Arrow D2 - Rotation direction two, Arrow D3 - Scanning direction one, Arrow D4 - Scanning direction two, Arrow D5 - Raw material deposition trajectory forward direction, D51 - Raw material deposition trajectory forward direction one, D52 - Raw material deposition trajectory forward direction two, D53 - Raw material deposition trajectory forward direction three, D101 - Translation direction one, D202 - Translation direction two, D303 - Translation direction three. Detailed Implementation

[0088] The preferred embodiments of the present invention are listed below, and the present invention will be described in detail with reference to the accompanying drawings.

[0089] like Figures 1 to 8The first specific embodiment of the present invention is a scanning laser printhead: a scanning laser printhead is provided with a laser interface (i.e., laser interface one 102, laser interface two 103, laser interface three 104 and laser interface four 105), a beam moving focusing lens group and a raw material transport channel (i.e., raw material transport channel 106).

[0090] The beam-shifting focusing lens assembly includes beam-shifting lenses and focusing lenses. There are four beam-shifting lenses (two of which are translation lens 2 118 and translation lens 4 121, the other two are not shown in the figures) and four focusing lenses (two of which are focusing lens 2 119 and focusing lens 4 122, the other two are not shown in the figures). The beam-shifting lenses and focusing lenses are independent components. The beam-shifting lenses are used to change the planar scanning position of the laser spot on the workpiece surface, and the focusing lenses are used to focus the laser beam to change the area of ​​the laser spot on the workpiece surface. In this embodiment, the beam-shifting lenses are located before the focusing lenses in the propagation path of the laser beam. Of course, in other embodiments, the beam-shifting lenses may also be located after the focusing lenses in the propagation path of the laser beam.

[0091] At least two laser beams can be projected. Correspondingly, the number of laser interfaces and beam-shifting focusing lens groups is the same as the number of laser beams. Each laser beam passes through one laser interface and one beam-shifting focusing lens group. Specifically, in this embodiment, the number of housings 101 is the same as the number of laser beams, that is, there are four housings 101, and the four housings 101 are integrally formed. Of course, in other embodiments, the four housings 101 can also be formed independently and then fixedly connected together. The two ends of the housing 101 are open. The upper opening of the housing 101 forms the laser interface, and the lower opening of the housing 101 forms the laser emission port. The beam-shifting focusing lens group is disposed inside the housing 101, and the housing 101 is assembled together with the raw material conveying channel 106. In this way, the laser interface, beam-moving lens, focusing lens, and raw material conveying channel are connected and combined into a whole by housing 101; a window mirror (two of which are window mirror 2 120 and window mirror 4 123, the other two are not shown in the attached figure) is set below each focusing lens in the laser path (i.e., the laser emission section). The window mirror is a protective mirror used to prevent external substances from entering the optical path and contacting the beam-moving focusing lens group, such as preventing dust from contaminating the focusing lens; each laser path passes through a set of components consisting of laser interface, beam-moving lens, focusing lens, and... The optical path unit is composed of a window mirror; a cooling chamber 110 is provided inside the housing 101. The cooling chamber 110 is located between the raw material conveying channel 106 and the four housings 101. The cooling chamber 110 is provided with two coolant inlets symmetrically distributed on both sides of the raw material conveying channel 106. Coolant (e.g., deionized water) enters the cooling chamber 110 through one side of the coolant inlet 107 and then flows out from the other side of the coolant inlet 107. The coolant inlet and the cooling chamber 110 form a liquid cooling passage for cooling the scanning laser print head.

[0092] The laser beam from the laser interface, after being modulated by the beam-moving focusing lens group, is projected onto the workpiece (i.e., workpiece 113) from the space surrounding the exit end of the raw material conveying channel (i.e., raw material conveying channel 106). Four laser beams (i.e., laser beam one 114, laser beam two 115, laser beam three 116, and laser beam four 117) can be projected. Each laser beam can be independently controlled; the number of laser beams projected simultaneously is controllable, the power of each laser beam can be independently controlled, and the scanning parameters of each laser beam can be independently controlled. Four semiconductor lasers (not shown in the figures) are used, each connected to a laser interface via a laser output head and supplying laser light to the scanning laser print head through the laser interface. The raw material required for printing arrives at the workpiece 113 via the raw material conveying channel 106. The raw material is solid (i.e., linear solid material 112), and the molten material formed after the solid material melts is deposited on the workpiece. Of course, in other embodiments, the raw material can also be a liquid material (e.g., using a micro furnace to output liquid material).

[0093] The aforementioned beam-shifting focusing lens assembly can be rotated and / or moved to modulate the position of the laser beam projected onto the workpiece, thereby causing the laser beam to scan and heat the edge and / or periphery of the area on the workpiece where material is being deposited; that is, the spot formed by the laser beam projected onto the workpiece moves along the edge and / or periphery of the area on the workpiece where material is being deposited. Specifically, in this embodiment, the position of the laser beam projected onto the workpiece is modulated by moving the beam-shifting lens, thereby causing the laser beam to scan and heat the edge and / or periphery of the area on the workpiece where material is being deposited. In other embodiments, the position of the laser beam projected onto the workpiece can also be modulated by rotating the beam-shifting lens; alternatively, the position of the laser beam projected onto the workpiece can also be modulated by rotating and moving the beam-shifting lens.

[0094] The area where the raw material is being deposited refers to the area on the workpiece that is in contact with the raw material being deposited; in this first specific embodiment, the front end of the linear solid raw material 112 is melted to produce molten raw material being deposited, and the area on the surface of the workpiece 113 that is in contact with the front end of the linear solid raw material 112 that is melted is the area where the raw material is being deposited.

[0095] The edge of the area where the raw material is being deposited refers to the edge of the area on the workpiece that is in contact with the raw material being deposited, such as... Figure 13 and Figure 15 The overlapping area 239 shown is part of the edge. The periphery of the area where the raw material is being deposited refers to the area on the workpiece that is adjacent to or connected to the area where the raw material is being deposited.

[0096] The aforementioned beam-moving lens can be translated or rotated in one dimension to make the laser beam move in one dimension; or, the aforementioned beam-moving lens can be translated or rotated in two dimensions to make the laser beam move in two dimensions.

[0097] In this first specific embodiment: before the front end of the linear solid material 112 is melted, the four laser beams have not yet started scanning and heating. The initial position of the laser spots on the surface of the workpiece 113 and the positional relationship between them and the linear solid material 112 are as follows: Figure 5 As shown; scanning range 124, scanning range 225, scanning range 3126, and scanning range 4127 are the scanning ranges of laser beam 114, laser beam 215, laser beam 316, and laser beam 417 on the surface of workpiece 113, respectively. The maximum scanning range of each laser beam is 180°, and the scanning range can be dynamically adjusted. Before the front end of the linear solid material 112 is melted, when the scanning range of each laser beam is set to 90°, the positional relationship between scanning range 124, scanning range 225, scanning range 3126, scanning range 4127 and the linear solid material 112 is as follows. Figure 6As shown: Scanning range 124, scanning range 225, scanning range 3126 and scanning range 4127 are combined to form a ring (i.e., a ring-shaped composite scanning area). Before the front end of the linear solid material 112 is melted, the inner edge of the ring is in contact with the circumferential surface of the front end of the linear solid material 112. That is, the projection of the ring and the linear solid material 112 on the surface of the workpiece 113 overlaps slightly (that is, the laser beam also heats the solid material outside the outlet of the material conveying channel 106). The linear solid material 112 is heated and melted by the laser energy distributed in the overlapping area (that is, molten material is generated in the space between the outlet of the material conveying channel 106 and the workpiece 113). The laser energy distributed in other areas of the ring heats the surface of the workpiece 113 to form a molten pool (not shown in the figure). Since the volume and surface area of ​​the workpiece are generally much larger than those of the tip of the linear solid material 112, and the workpiece 113 and the substrate to which it is attached also dissipate heat to the molten pool, the heat required to melt the tip of the linear solid material 112 is generally significantly less than the heat required to melt the workpiece surface to generate the molten pool (the specific ratio depends on factors such as printing speed, material type, laser wavelength, intensity of gas toxicity, ambient temperature, and heat dissipation conditions). After the tip of the linear solid material 112 is heated and melted, it immediately deposits on the workpiece 113. The area on the workpiece 113 in contact with the depositing material is the area where the material is being deposited. Figure 6 The annular composite scanning area, formed by scanning range 124, scanning range 125, scanning range 126, and scanning range 127, shown in the diagram, surrounds the area on the workpiece 113 where material is being deposited. That is, when two or more laser beams are simultaneously projected onto the workpiece, the scanning areas of the laser beams on the workpiece form a composite scanning area that surrounds the area on the workpiece where material is being deposited. When scanning range 124 is scanned and heated by laser beam 114, the surface of workpiece 113 containing scanning range 124 becomes the scanning and heating area of ​​laser beam 114 on workpiece 113. Similarly, when scanning ranges 125, 126, and 127 are all scanned and heated by their respective laser beams, they all belong to the corresponding scanning and heating areas of their respective laser beams on workpiece 113. During the 3D printing process, the entire scanning and heating area moves relative to workpiece 113 along with the scanning laser printhead in this specific embodiment (with workpiece 113 as the reference point for movement).

[0098] In this first specific embodiment, the focusing lens is a non-field focusing lens, using a common focusing lens, such as the focusing lens used in the cutting head of a laser cutting machine; of course, in other embodiments, the focusing lens can also be a field focusing lens. (Explanation: A field focusing lens, also called a flat field focusing lens or f-theta focusing lens, is a specialized lens system whose function is to form a uniformly sized focused spot of the laser beam across the entire marking plane, and it is one of the most important components of a laser marking machine.)

[0099] The beam-moving lens can be driven by electromagnetic force (e.g., electric motor or electromagnet), piezoelectric element (e.g., piezoelectric ceramic), thermo-deformation (e.g., a drive mechanism using thermo-deformation material as the driving component), magneto-deformation (e.g., a drive mechanism using magneto-deformation material as the driving component), electro-deformation (e.g., a drive mechanism using electro-deformation material as the driving component), or fluid drive (e.g., cylinder drive, hydraulic push rod drive). The specific method used to drive the beam-moving lens can be selected as needed.

[0100] In this first specific embodiment, the beam-moving lenses (there are four, two of which are translation lenses 118 and 121, and the other two are not shown in the figures) use a translation method to move the laser beam, that is, when the laser beam passes through the moving lens, the laser beam exits the lens and follows the movement. All four translation lenses (beam-moving lenses) adopt the same structure, such as... Figure 7 and Figure 8As shown: It consists of a concave lens 128, a housing 129, an electromagnet 130, a permanent magnet 131, a spring 132, an electromagnet 2 133, a permanent magnet 2 134, a spring 2 135, an electromagnet 3 136, a permanent magnet 3 137, and a spring 3 138. Permanent magnets 131, 134, and 137 are fixed on the outer circumference of the concave lens 128, dividing the outer circumference of the lens 128 into three equal parts (i.e., distributed at 120° intervals). Springs 132, 135, and 138 connect the concave lens 128 to the housing 129, further dividing the outer circumference of the lens 128 into three equal parts (i.e., distributed at 120° intervals). Electromagnet 136, 137, and 138... 30. Electromagnets 133 and 136 are fixed on the inner circumference of the outer shell 129 and the inner circumference of the outer shell 129 is divided into three equal parts (i.e., distributed at 120° intervals). Electromagnets 130, 133, and 136 are paired with permanent magnets 131, 134, and 137, respectively. When electromagnets 130, 133, and 136 are energized, they will generate magnetic attraction or repulsion with permanent magnets 131, 134, and 137, respectively. The specific repulsion or attraction depends on the direction of the current flowing through electromagnets 130, 133, and 136. Translation direction one (D101), translation direction three (D303), and translation direction two (D202) represent the translations produced by the interactions between electromagnet one 130 and permanent magnet one 131, electromagnet two 133 and permanent magnet two 134, and electromagnet three 136 and permanent magnet three 137, respectively. By controlling the current intensity and direction flowing through electromagnet one 130, electromagnet two 133, and electromagnet three 136, a radial motion vector pointing in any direction within the radial plane of the concave lens 128 can be synthesized, thereby achieving the translation of the laser beam passing through the concave lens 128. The method of driving the concave lens 128 to move within the radial plane is electromagnetic force driven.

[0101] In this first specific embodiment, a gas interface (a total of 4, of which 3 are gas interface 108, gas interface 109, and gas interface 411, and the remaining one is not shown in the figure) is provided below each window mirror (i.e., the laser emission port) on the laser path. The gas interface, the inner cavity of housing 101 and the laser emission port constitute the gas path. Protective gas enters the inner cavity of housing 101 from the gas interface and is ejected from the laser emission port. The gas path is used to spray gas to form a gas curtain to prevent or reduce the contamination of optical components (beam moving focusing lens group and window mirror) by external substances (such as dust and metal vapor). In addition, the gas path can also be used to spray protective gas on the depositing raw material and the molten pool on the workpiece to form a protective atmosphere.

[0102] In this first specific embodiment, when printing the first layer of a metal part, that is, the first layer of the workpiece, printing is done on a metal substrate. For example, the first layer of a stainless steel part is printed on a stainless steel plate or a metal plate that can be welded to stainless steel.

[0103] like Figure 9 As shown, the second specific embodiment of the present invention is similar to... Figures 1 to 8 The first specific embodiment of the scanning laser printhead of the present invention shown all uses four independently controllable laser beams. The difference is that the beam moving focusing lens group of the first specific embodiment includes a beam moving lens and a focusing lens, while the beam moving focusing lens group of this embodiment does not include a beam moving lens, but is composed of at least one focusing lens that can be rotated and / or moved. The focusing lens is used to move and focus the laser beam. By rotating and / or moving the focusing lens, the position of the laser beam projected on the workpiece is modulated, so that the laser beam scans and heats the edge and / or periphery of the area on the workpiece where the raw material is being deposited.

[0104] The focusing lens can be translated or rotated in one dimension to move the laser beam in one dimension; or, the focusing lens can be translated or rotated in two dimensions to move the laser beam in two dimensions; or, the focusing lens can be translated or rotated in two dimensions to move the laser beam in one dimension and to focus the focusing lens; or, the focusing lens can be translated or rotated in three dimensions to move the laser beam in two dimensions and to focus the focusing lens.

[0105] Specifically, such as Figure 9As shown: This beam-shifting focusing lens assembly consists of two focusing lenses, each a rotatable convex lens (i.e., rotating lens 139 and rotating lens 141). The two focusing lenses are sequentially positioned along the propagation path of the laser beam, each rotating about its own axis, which are perpendicular to each other. Rotating lens 139 rotates radially about axis 140, in the direction shown in rotation direction D1; rotating lens 141 rotates radially about axis 142, in the direction shown in rotation direction D2. When the incident beam 143 passes through rotating lens 139, under the rotational control of rotating lens 139, a first-stage scanning beam 144 is generated; the second... When the primary scanning beam 144 passes through the rotating lens 141, the second scanning beam 145 is generated under the rotation control of the rotating lens 141. The second scanning beam 145 can perform two-dimensional scanning, as shown in scanning direction one D3 and scanning direction two D4. The rotating lens 139 rotates about the rotating shaft 140 as the radial rotation axis to generate scanning in the direction shown in scanning direction one D3. The rotating lens 141 rotates about the rotating shaft 142 as the radial rotation axis to generate scanning in the direction shown in scanning direction two D4. Both the rotating lens 139 and the rotating lens 141 are driven by electromagnetic force and are driven by galvanometer motors. The rotating shafts 140 and 142 are respectively connected to the shaft of a galvanometer motor.

[0106] The third specific embodiment of the present invention (without drawings) is in Figures 1 to 8 Based on the first specific embodiment of the scanning laser printhead of the present invention shown, two sets of optical path units composed of laser interface, beam moving lens, focusing lens and window lens are removed. The remaining two sets of optical path units are symmetrically distributed on both sides of the raw material conveying channel, using two sets of semiconductor lasers and two laser paths, with the other structures being completely identical.

[0107] The fourth embodiment of the present invention (without accompanying drawings) is based on the third embodiment of the present invention, but replaces the semiconductor laser with a fiber laser, using two fiber lasers. The diverging light output from the laser output head is collimated by a collimating lens and then enters the optical path unit of the third embodiment of the present invention through a laser interface, and finally projects onto the workpiece.

[0108] When the number of projected laser beams is two or more, the power of each laser beam can be independently controlled; when the number of projected laser beams is two or more, the scanning parameters of each laser beam can be independently controlled. Taking the first specific embodiment of the present invention as an example, parameters such as the shape and area of ​​the scanning region of each laser beam, the scanning rate, the average power density of the laser spot in the scanning region, the dwell time of the laser spot at certain positions during the scanning process, the curve shape of the scanning path, and the degree of overlap between the scanning region and the region where the raw material is being deposited are adjusted. Figures 10 to 15 As shown.

[0109] exist Figure 10 In the figure, a composite scanning area is formed by combining two scanning areas (i.e., scanning mode 1 237 and scanning mode 2 238). The curved shape of the laser scanning path is shown by the lines in the figure. Arrow D5 indicates the deposition direction of the material on the workpiece surface. The projection 146 of the linear solid material on the workpiece surface is connected to the composite scanning area but does not overlap. The composite scanning area is an open ring, that is, it is not a complete ring and does not fill the 360° area around the projection 146 of the linear solid material on the workpiece surface. The front end of the linear solid material is melted to produce molten material that is being deposited. The area on the workpiece surface that is in contact with the melted front end of the linear solid material is the area where the material is being deposited. The area where the material is being deposited is also surrounded (not completely surrounded) by the composite scanning area.

[0110] exist Figure 11 In the figure, a composite scanning area is formed by combining two scanning areas (i.e., scanning mode three 240 and scanning mode four 241). The curved shape of the laser scanning path is shown by the lines in the figure. Arrow D5 indicates the deposition direction of the material on the workpiece surface. The projection 146 of the linear solid material on the workpiece surface is not directly connected to the composite scanning area; they are adjacent and do not completely occupy the 360° area centered on the projection 146 of the linear solid material on the workpiece surface. The front end of the linear solid material is melted to produce molten material that is being deposited. The area on the workpiece surface that is in contact with the melted front end of the linear solid material is the area where the material is being deposited, and the area where the material is being deposited is also surrounded (not completely surrounded) by the composite scanning area.

[0111] exist Figure 12In the diagram, a composite scanning area is formed by combining three scanning zones (i.e., scanning pattern 5 242, scanning pattern 6 243, and scanning pattern 7 244). Scanning pattern 6 243 has the highest scanning density, resulting in the highest energy accumulation of the laser within this zone. Scanning pattern 7 244 has the lowest scanning density. The curved shape of the laser scanning path is shown in the figure, with arrow D5 indicating the deposition direction of the material on the workpiece surface. The projection 146 of the linear solid material on the workpiece surface is not directly connected to the composite scanning area; they are adjacent and occupy a 360° perimeter centered on the projection 146 of the linear solid material on the workpiece surface. The leading edge of the linear solid material is melted, generating molten material that is being deposited. The area on the workpiece surface in contact with the melted leading edge of the linear solid material is the area where the material is being deposited, and this area is also completely surrounded by the composite scanning area. The laser power densities in the three scanning regions—Scanning Mode 5 (242), Scanning Mode 6 (243), and Scanning Mode 7 (244)—are different, creating unique thermal fields. These fields influence the shape and thermal field of the molten pool formed by the laser beam heating the workpiece (i.e., the printed object), thus affecting the 3D printing process and the material properties of the final part. Scanning Mode 7 (244) uses lower power, only heating the surface of the workpiece (printed object) and the freshly deposited material. This creates a "heat-preserving effect," insufficient to vaporize or partially vaporize the freshly deposited material. This achieves a smoother surface while avoiding the serious problems caused by overheating, such as significant vaporization, from high-power heating of the freshly deposited material.

[0112] exist Figure 13In this system, there is only one scanning area (i.e., scanning pattern eight, area 245). The curved shape of the laser scanning path is shown by the lines in the figure, with arrow D5 indicating the deposition direction of the material on the workpiece surface. The scanning area is triangular in shape. The front end of the linear solid material is melted to produce molten material being deposited. The area on the workpiece surface that contacts the melted front end of the linear solid material is the area where the material is being deposited, and this area is also surrounded (semi-enclosed) by scanning pattern eight, area 245. There is an overlap area, namely overlap area 239, between scanning pattern eight, area 245 and the projection 146 of the linear solid material on the workpiece surface. Overlap area 239 is the edge of the material being deposited. In other words, the laser beam is controlled by the moving focusing lens group to heat the edge of the material being deposited, thereby transferring heat through the material to the edge of the area where the material is being deposited on the printed body, thus achieving edge scanning and heating of the area where the material is being deposited on the printed body. The laser beam heats the linear solid material through overlap area 239, and the intensity of the heating effect mainly depends on the area of ​​this overlap area. When the forward direction of the raw material deposition path in 3D printing is in the positive direction of one side of the scanning pattern 245 region (i.e., the direction shown by arrow D5), the raw material that has just been deposited will not be reheated by the laser, thus avoiding serious problems caused by overheating. For example, the high fluidity of the raw material after deposition can lead to reduced shape controllability and molding accuracy. It can also cause significant vaporization, resulting in changes in material composition (different components in the alloy material have different boiling points, resulting in more evaporation of components with lower boiling points, such as aluminum in TiAl6V4 titanium alloy being more easily vaporized than titanium), and the generation of micropores inside the material (leading to a reduction in the performance of the final part).

[0113] exist Figure 14 In this design, there is only one scanning area (i.e., scanning pattern nine, area 246), which is circular and scanned using four laser beams. Each laser beam is responsible for a 90° area (i.e., a quarter-area). The curved shape of the laser scanning path is shown by the lines in the figure, and each laser beam's scanning path (i.e., scanning trajectory) is a 90° arc. Arrow D5 indicates the deposition direction of the material on the workpiece surface. The inner boundary of the circular scanning area is connected to the projection 146 of the linear solid material on the workpiece surface. The leading edge of the linear solid material is melted to produce molten material that is being deposited. The area on the workpiece surface that is in contact with the melted leading edge of the linear solid material is the area where the material is being deposited, and this area is also surrounded by scanning pattern nine, area 246 (360° encirclement).

[0114] exist Figure 15In this system, there is only one scanning area (i.e., scanning pattern + 247 region). The scanning area is distributed along the deposition path of the raw material on the workpiece surface and is a region connected to the projection 146 of the linear solid raw material on the workpiece surface but where the raw material has not yet been deposited (i.e., the region where the raw material is about to be deposited). The forward direction of the raw material deposition trajectory - D51, the forward direction of the raw material deposition trajectory - D52, and the forward direction of the raw material deposition trajectory - D53 represent the forward vectors of the three segments of the raw material deposition path. The total length of these three segments of the raw material deposition path is approximately 3.5 times the diameter of the projection 146 of the linear solid raw material on the workpiece surface. The total length can be set in the laser scanning parameters. There is an overlap area 239 between the scanning pattern 247 region and the projection 146 of the linear solid material on the workpiece surface. The overlap area 239 is the edge of the material being deposited. That is, the beam moving focusing lens group controls the laser beam to heat the edge of the material being deposited (i.e., the light spot formed by the laser beam projected onto the material being deposited moves along the edge of the material being deposited), thereby conducting heat through the material being deposited to the edge of the area where the material is being deposited on the printed body, thus achieving edge scanning heating of the area where the material is being deposited on the printed body. The front end of the linear solid material is melted to produce molten material being deposited. The area on the workpiece surface that contacts the melted front end of the linear solid material is the area where the material is being deposited. The area where the material is being deposited is also surrounded by the scanning pattern 247 region (180° surround / semi-surround). This scanning pattern 247 can preheat the area where the material is about to be deposited, reduce the temperature gradient between the area where the material is being deposited and other areas of the workpiece (printed body), suppress the generation of thermal cracks, and improve the material properties (mainly mechanical properties, such as the fatigue resistance of metal parts) of 3D printed parts or welded parts. Existing metal 3D printing technologies, especially Selective Laser Melting (SLM) and Direct Energy Deposition (DED) (existing coaxial and off-axis 3D printing systems based on laser heating, off-axis 3D printing systems based on electric arc heating, and coaxial and off-axis powder feeding 3D printing systems based on laser heating all belong to DED technology), generally suffer from low fatigue resistance of parts, which is a huge obstacle restricting the application of existing metal 3D printing technologies in industrial production.

[0115] visible, Figure 10 and Figure 14 The laser beam is used to scan and heat the periphery of the area on the printed body where the material is being deposited. Specifically, the laser beam scans and heats the area on the printed body that is connected to the area where the material is being deposited. Figure 11 and Figure 12The laser beam is used to scan and heat the periphery of the area on the printed body where the material is being deposited. Specifically, the laser beam scans and heats the area on the printed body adjacent to the area where the material is being deposited. Figure 13 and Figure 15 The laser beam scans and heats both the edges and periphery of the area on the printed body where material is being deposited. Of course, in other scanning and heating methods, only the edges of the area on the printed body where material is being deposited (i.e., the area indicated by reference numeral 239) can be scanned and heated.

[0116] like Figures 10 to 15 The scanning heating method shown in the figure involves a laser scanning and heating the surface of the printed object to generate a molten pool. Because the "scanning heating" method can "stir" the molten pool, it can have a beneficial effect on the performance of the final 3D printed part, such as reducing micropores.

[0117] Other preferred embodiments of the present invention include: a collimating lens is provided to convert a non-parallel laser beam into a parallel laser beam, for example, to convert diverging laser light from a fiber laser into parallel light. The collimating lens is located before the laser interface in the propagation path of the laser beam.

[0118] For example, a beam splitter is used to split a laser beam into at least two beams, allowing a single laser to generate multiple laser beams. The beam splitter is positioned before the laser interface along the propagation path of the laser beams.

[0119] For example, a gas passage for spraying inert gas can be provided. For instance, vents can be provided around the lower end outlet of the raw material conveying channel 106 in the first specific embodiment. The inert gas sprayed from the vents can spray protective gas onto the raw material and the molten pool on the workpiece to form a protective atmosphere (e.g., argon gas can be sprayed into the space where the raw material and the molten pool are located to form an inert gas protective atmosphere).

[0120] For example, setting up an optical path switching component to switch the laser beam from one propagation path to another (e.g., using a motor to drive a reflector to control the laser propagation path, achieving "time-division multiplexing").

[0121] For example, the focusing lens is adjustable, and the focusing method can be manual focusing, electric focusing, pneumatic focusing, or hydraulic focusing. Among them, electric focusing based on two-dimensional translation and / or two-dimensional rotation can realize three-dimensional scanning heating.

[0122] For example, the number of projected laser beams is at least two, one of which scans and heats the edge and / or periphery of the area on the workpiece where the raw material is being deposited to generate a molten pool, while the other laser beam trims the shape of the already printed workpiece surface.

[0123] Because the existing laser "coaxial wire feeding" heating method is the same as the "heat conduction method" of laser welding (the existing laser coaxial wire feeding metal 3D printing is essentially based on laser welding), that is, the laser spot power density range is the same as that of traditional heat conduction laser welding. The spot power density value cannot produce significant vaporization, otherwise it will seriously damage the 3D printing process. Therefore, it is impossible to increase the spot power density to achieve the "laser cleaning" function. However, the present invention uses a scanning heating method, which can rapidly disperse heat over a larger area. It can diffuse heat without relying on the "heat conduction" method. Therefore, a higher power density laser beam can be used to simultaneously achieve "laser cleaning" while heating to generate a molten pool. This removes substances harmful to 3D forming (such as oxide film) from the molten pool and the surface of the molten material. Combined with resistance heating and other methods to generate molten material, it can counteract the toxic effects of air on the 3D forming process. Preferably, the laser beam can be used to scan and heat the interface between the workpiece surface and the material being deposited to perform laser cleaning on the interface. Therefore, the present invention can achieve 3D printing in air without the use of a protective gas. Laser cleaning, also known as laser ablation or photoablation, is a process that removes material from a solid (or sometimes liquid) surface by irradiating it with a laser beam. The surface material is heated by the absorbed laser energy and evaporates or sublimates. Typically, laser cleaning refers to removing a thin layer of material from the surface of an object using a pulsed laser without damaging the underlying structure. In rare cases, continuous laser ablation can be used to remove thin layers of material from the surface of an object, but due to the extremely high energy of continuous lasers, the thermal effects are very severe, for example, causing remelting of solid metal surfaces, i.e., creating a molten pool (thin molten pool) while ablating the metal. This invention utilizes the characteristic of continuous lasers to generate a molten pool when used as a heat source for laser cleaning.

[0124] The above description is only a preferred embodiment of the present invention and should not be construed as limiting the scope of the present invention. All equivalent transformations and modifications made based on the claims and description of the present invention shall still fall within the scope of the present invention.

Claims

1. A scanning laser printing head, characterized in that: a laser interface, a beam moving and focusing lens group and a raw material delivery channel are provided, a laser beam from the laser interface is modulated by the beam moving and focusing lens group and then projected from the surrounding space of the raw material delivery channel to a workpiece; a raw material required for printing reaches the workpiece through the raw material delivery channel, the raw material is in a liquid or solid state, and a molten raw material formed after the liquid or solid raw material is melted is deposited on the workpiece; the beam moving and focusing lens group can rotate to modulate the position of the laser beam projected on the workpiece, so that the laser beam scans and heats the edge and / or periphery of the area of the workpiece where the raw material is being deposited; while the laser beam scans and heats the edge and / or periphery of the area of the workpiece where the raw material is being deposited, the scanning and heating area of the laser beam on the workpiece moves relative to the workpiece; the number of laser beams that can be projected is at least two; each laser beam can be independently controlled; the number of laser beams projected at the same time is controllable; correspondingly, the number of the laser interface and the beam moving and focusing lens group is the same as the number of laser beams, and each laser beam passes through one laser interface and one beam moving and focusing lens group; the area of the raw material being deposited refers to the area of the workpiece that is in contact with the raw material being deposited; the edge of the area of the raw material being deposited refers to the edge of the area of the workpiece that is in contact with the raw material being deposited; the periphery of the area of the raw material being deposited refers to the area of the workpiece adjacent or connected to the area of the raw material being deposited; the beam moving and focusing lens group is composed of at least one rotatable focusing mirror, the focusing mirror is used for moving and focusing the laser beam, and the focusing mirror rotates around its radial rotation axis, the position of the laser beam projected on the workpiece is modulated by rotating the focusing mirror, so that the laser beam scans and heats the edge and / or periphery of the area of the workpiece where the raw material is being deposited.

2. The scanning laser printing head according to claim 1, characterized in that: the focusing mirror can rotate in one dimension to make the laser beam move in one dimension; or the focusing mirror can rotate in two dimensions to make the laser beam move in two dimensions.

3. The scanning laser printing head according to claim 1, characterized in that: the beam moving and focusing lens group comprises two lens groups, the two lens groups are arranged in sequence on the propagation path of the laser beam, the two lens groups rotate around their respective rotation axes, and the rotation axes of the two lens groups are arranged perpendicular to each other.

4. The scanning laser printing head according to claim 3, characterized in that: each lens group comprises at least one lens, the lens is a convex lens or a concave lens, and at least one of the two lens groups is a convex lens as a focusing mirror.

5. The scanning laser printing head according to claim 1, characterized in that: when the raw material is in a solid state, the laser beam also heats the solid raw material outside the outlet of the raw material delivery channel to generate a molten raw material in the space between the outlet of the raw material delivery channel and the workpiece.

6. The scanning laser printing head according to claim 1, characterized in that: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ When the number of laser beams projected on the workpiece is two or more, the spot scanning areas of the laser beams on the workpiece can form a composite scanning area, which can surround the area on the workpiece where the feedstock is being deposited.

7. The scanning laser head according to claim 1, wherein: the laser beams scan the edge and / or the periphery of the area on the workpiece where the feedstock is being deposited to generate a molten pool; when the number of laser beams projected is two or more, the power of each laser beam can be independently controlled; when the number of laser beams projected is two or more, the scanning parameters of each laser beam can be independently controlled.

8. The scanning laser head according to claim 1, wherein: the focusing mirror is a field lens focusing mirror or a non-field lens focusing mirror; the focusing mirror is driven by electromagnetic force, or by a piezoelectric element, or by thermal deformation, or by magnetic deformation, or by electric deformation, or by fluid.

9. The scanning laser head according to claim 1, wherein: a collimating mirror is provided to convert a non-parallel laser beam into a parallel laser beam, the collimating mirror being located before the laser interface in the propagation path of the laser beam; a beam splitter is provided to split one laser beam into at least two laser beams, the beam splitter being located before the laser interface in the propagation path of the laser beam; a window mirror is provided to block external substances from contacting the beam moving focusing lens group; a gas passage is provided to inject gas to form a gas curtain, through which external substances are prevented or mitigated from contaminating the beam moving focusing lens group and the window mirror, and / or to inject a protective gas to form a protective atmosphere for the feedstock being deposited and the molten pool on the workpiece; a liquid cooling passage is provided to cool the scanning laser head; a light path switching assembly is provided to switch the laser beam from one laser interface to another laser interface.

10. The scanning laser head according to claim 1, wherein: the same number of housings as the laser beams are further included, the housings being through at both ends, the upper end opening of the housing forming the laser interface, and the lower end opening of the housing forming a laser exit port, the beam moving focusing lens group being arranged in the housing, and the housing being attached to the feedstock delivery channel.

11. The scanning laser head according to claim 1, wherein: the focusing mirror is adjustable in focus, and the focus adjustment is manual, or electric, or pneumatic, or hydraulic.

12. The scanning laser head according to claim 1, wherein: the laser interface is connected to the laser output head of a laser.

13. The scanning laser head according to claim 1, wherein: the area on the feedstock deposition path of the workpiece that is scanned by the laser beams to be heated to form a molten pool can be preheated in advance, and the preheating range can be set.

14. The scanning laser head of claim 1, wherein: the beam movement focusing lens group controls the laser beams to heat the edge of the area of the material being deposited to conduct heat through the material being deposited to the edge of the area of the material being deposited on the build.

15. The scanning laser head of claim 1, wherein: the number of laser beams projected is at least two, wherein a portion of the laser beams are scanned to heat the edge and / or perimeter of the area of the material being deposited on the workpiece to create a melt pool and another portion of the laser beams are scanned to modify the topography of the surface of the workpiece that has been printed on the workpiece.

16. The scanning laser head of claim 1, wherein: the beam movement focusing lens group controls the laser beams to heat the material being deposited while the laser beams are scanned to heat the edge and / or perimeter of the area of the material being deposited.

17. The scanning laser head of claim 1, wherein: the laser beams are scanned to heat the interface between the surface of the workpiece and the material being deposited to laser clean the interface.

Images