Water hammer type on-demand injection-laser coaxial composite material increasing device and method

Abstract

The invention discloses a water hammer type molten drop on-demand spraying-laser coaxial composite additive manufacturing device and method, and relates to the field of metal additive manufacturing. A water hammer type molten drop on-demand spraying device and an annular laser light source composed of a plurality of laser units are coaxially integrated, laser power distribution planning is carried out according to a deposition path, and metal component additive manufacturing is achieved through molten drop spraying; and the bonding effect between the adjacent molten drops and the bonding effect between the molten drops and the substrate are improved through coaxial composite laser heating. According to the device and the method, the mechanical property of a component manufactured through the molten drop spraying type metal additive manufacturing method can be improved, meanwhile, the defect that when a single paraxial laser beam is used, the performance of a deposition material is changed due to the fact that the direction of a deposition path is changed is overcome, and due to the use of the water hammer type on-demand spraying device, the device integrated with the annular laser light source is compact in structure; the total volume is small, and the application value is high.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal additive manufacturing, and in particular relates to a water hammer type on-demand injection-laser coaxial composite additive device and method. Background Art

[0002] Metal additive manufacturing offers a tremendous opportunity for the development and transformation of the manufacturing industry. Among them, metal additive manufacturing technology, which uses lasers as an energy source, can achieve high-density, near-net-net-net shapes for complex components and is currently the most mature commercial additive manufacturing technology. However, the extremely high cooling rate of materials in laser additive manufacturing can lead to deformation, cracking, and other problems in the printed components. Furthermore, laser additive manufacturing also carries high equipment and raw material costs, which to some extent limit the development and application of laser additive manufacturing. Compared with laser additive manufacturing, droplet jetting directly melts the metal in a liquid reservoir and then ejects it as droplets onto a substrate. This avoids excessive cooling of the material and has lower equipment and material costs, resulting in increasing attention. Based on the form of droplet ejection, droplet jetting can be divided into continuous jetting and on-demand jetting. On-demand jetting, which produces one droplet per drive signal, is more conducive to controlling forming accuracy and is therefore the primary development direction for droplet jetting. At present, researchers have proposed a variety of driving methods for metal droplet injection, including piezoelectric drive, pneumatic drive, electromagnetic drive, etc. The basic principle is to generate pressure pulses in a relatively closed liquid storage chamber to drive the droplet injection.

[0003] Although droplet jetting metal additive manufacturing has many advantages, there is a conflict between the mechanical properties and forming accuracy of the manufactured components. In order to achieve high-precision component manufacturing, the droplets need to be small in size and the droplet deposition density cannot be too high, otherwise there will be a large proportion of overlap between the droplets, which is not conducive to controlling the forming accuracy. However, smaller droplets have a larger specific surface area and therefore have a faster cooling rate, resulting in deterioration of the bonding between the droplets and reduced mechanical properties of the component. To solve this problem, more heat input is needed to the droplets and their deposition area to extend their cooling time. One approach is to improve the process parameters of the droplet jetting process itself, such as increasing the temperature of the molten metal in the liquid storage chamber and increasing the preheating temperature of the substrate. However, the heat input increments of these two methods are respectively provided to all the molten metal in the liquid storage chamber and all the deposited metal, rather than being provided separately to the depositing droplets and their surrounding areas, resulting in low energy utilization. Another approach is to provide heat separately to the depositing droplets and their surrounding areas through an external heat source. CN110722163A discloses a system and method for forming a dissimilar metal composite structure, combining droplet injection with a TIG arc heat source, using the arc to heat the deposited droplets, and achieving direct composite of dissimilar metals. However, the arc heat source not only provides arc heat, but also generates arc force, which can cause the trajectory of the droplet to deviate. This phenomenon is more obvious when the droplet size is small, and the fluctuation of the arc makes the droplet trajectory deviation difficult to predict and therefore difficult to compensate. CN117399652A discloses a metal additive manufacturing method and metal additive system with laser-induced control of forming size, combining droplet injection with laser, using the laser to heat the deposited droplets to improve forming accuracy. However, this method uses a single off-axis laser to heat the droplet, which is affected by directionality. That is, when the direction of the deposition path changes, the relative direction of the laser and the path being deposited will change, and the properties of the deposited material will also change accordingly, thereby affecting the uniformity of the component performance.

[0004] In order to eliminate the influence of directionality, multiple paraxial laser beams can be integrated in a circular manner. However, there are the following problems when directly integrating multiple paraxial laser beams with a droplet injection device. First, the method of integrating multiple paraxial laser beams in a circular manner has been adopted in traditional laser additive manufacturing, and most existing solutions distribute the total laser power evenly to each paraxial laser beam. Since the laser power used in laser additive manufacturing is relatively large, the metal material near the irradiated area can be completely melted, thus achieving good interlayer and interpass bonding. However, for droplet injection additive manufacturing, in order to maintain its advantage of moderate material cooling rate, the main purpose of adding lasers is not to completely melt the metal material, but to preheat and keep the deposited metal material warm, so the total laser power used is relatively small. When the total power is small, the power distribution of multiple laser beams needs to be more precise to achieve good interlayer and interpass bonding, rather than simply distributing the total power evenly to each laser beam. Secondly, among the existing droplet injection methods, the piezoelectric drive and electromagnetic drive methods can achieve higher injection frequencies and have better application prospects. However, these two methods require the use of pistons, permanent magnets, coils, etc., respectively, and the device volume is relatively large. In order to prevent the droplets from solidifying before being deposited on the substrate, the droplet injection device needs to be close enough to the substrate. Therefore, the laser light source cannot be integrated below the droplet injection device and can only be integrated on its periphery, which will further increase the volume of the entire device and is not conducive to its application and promotion. In addition, the larger device volume will also cause the laser light source to be farther away from the injection axis. When the height of the device from the substrate is constant, the farther the laser light source is from the injection axis, the greater the angle between the axis of the light source and the injection axis, the larger the irradiation area of ​​the laser on the workpiece surface, and the lower the energy density received on the workpiece surface, which is not conducive to the laser effect.

[0005] The above two problems can be solved respectively through the following ideas. In order to solve the power distribution problem of multiple laser beams, planning can be carried out according to the deposition path to achieve good inter-layer and inter-track bonding. In order to solve the problem of the layout space of the laser light source, CN116786838A discloses a high-melting-point metal droplet on-demand injection device and method using the water hammer effect. This method uses the water hammer pressure wave generated when the fluid velocity suddenly changes to drive the droplet injection. There is no need to arrange a piston inside the molten metal, nor is there a need for external complex permanent magnets and coils. While achieving efficient and high-precision droplet injection, it can maintain the compactness of the overall structure and provide conditions for the integration of multiple paraxial lasers in space. Based on the above ideas, the present invention proposes a water hammer on-demand injection-laser coaxial composite additive device and method, which suppresses the directionality of a single laser beam by integrating multiple paraxial lasers in a ring, achieves good inter-layer and inter-track bonding by performing laser power distribution planning, and obtains printed components with good mechanical properties. Summary of the Invention

[0006] In response to the above-mentioned problems existing in the prior art, the present invention proposes a water hammer type on-demand injection-laser coaxial composite additive device and method, which has a reasonable design, solves the shortcomings of the prior art, and has good effects.

[0007] In order to achieve the above-mentioned purpose 1 of the invention, the following technical solutions are adopted:

[0008] A water hammer type on-demand jetting-laser coaxial composite additive device, comprising a water hammer type on-demand jetting device, a ring-type laser light source, a control unit and a base plate;

[0009] The water hammer type on-demand injection device is used to melt the metal and realize on-demand injection of molten droplets by utilizing the water hammer pressure wave generated when the fluid velocity suddenly changes;

[0010] The annular laser light source is composed of at least three laser units distributed symmetrically around the circumference, with the axis of symmetry being the injection axis of the water hammer type on-demand injection device, and the lasers emitted by the multiple laser units are focused at a certain distance below the nozzle;

[0011] The substrate is located below the nozzle and can move in three dimensions;

[0012] The control unit is used to synchronously control the on-demand injection of the water hammer type on-demand injection device and the movement of the substrate, and independently control the light output and power of each laser unit.

[0013] Furthermore, the water hammer type on-demand injection device includes a nozzle, an actuator and a heating element. The upper end of the nozzle is connected to the actuator, and a nozzle hole is opened at the bottom end. The heating element can melt the metal in the nozzle. When the actuator drives the nozzle to perform a reciprocating motion along the axis with a micron-level stroke, the water hammer pressure wave caused by the sudden change in fluid velocity near the nozzle hole can cause the molten metal to produce an on-demand injection.

[0014] Furthermore, the annular laser light source adopts continuous laser or pulsed laser. When pulsed laser is adopted, the laser power is adjusted by adjusting the duty cycle of the pulse.

[0015] In order to achieve the above-mentioned purpose 2 of the invention, the following technical solutions are adopted:

[0016] A water hammer type on-demand jetting-laser coaxial composite additive method, using the water hammer type on-demand jetting-laser coaxial composite additive device as described above, performs additive manufacturing processing through the following steps:

[0017] Step 1: The control unit reads the three-dimensional model of the component to be processed and performs processing path planning and laser power distribution planning. The processing path planning is to divide the component to be processed into multiple layers for layered processing;

[0018] Step 2: The control unit adjusts the height of the substrate in the vertical direction so that the laser focus of the annular laser light source is located on the upper surface of the substrate. If the first layer is to be deposited, the substrate is the substrate; otherwise, the substrate is the deposited component.

[0019] Step 3: The control unit synchronously controls the on-demand injection of the water hammer on-demand injection device and the movement of the substrate in the horizontal plane according to the processing path planned in step 1. Based on the laser power distribution planning results in step 1, the control unit turns on the circular laser light source and adjusts the power of each laser unit to heat the molten droplet currently deposited on the upper surface of the substrate and the surrounding area to achieve good interlayer bonding and inter-pass bonding within the same layer.

[0020] Step 4: Repeat steps 2 and 3 to complete the manufacturing of the component layer by layer.

[0021] Furthermore, in step 1, laser power allocation planning is performed through the following sub-steps:

[0022] Step 11: Set the interlayer laser power P layer and inter-channel laser power P pass , the inter-layer laser power should be greater than the inter-channel laser power;

[0023] Step 12: According to the processing path planning, the processing path is discretized into a series of points, and the laser power is calculated point by point. The current planned point is recorded as O, and an empty set S is established. If the deposition path where point O is located is the first deposition path in the layer, jump directly to step 13. Otherwise, the deposition path of the deposition path adjacent to the deposition path where point O is located in the layer is recorded as L, and the normal line of L is generated from point O and recorded as The direction is from O to L; the total number of laser units in the annular laser light source is N, and the center point of the laser spot irradiated by each laser unit on the upper surface of the substrate is C k , k=1,2,…,N, calculate each vector and The angle α k , if α k ≤90°, then add k to the set S;

[0024] Step 13: For each point on the processing path, record the power of the kth laser unit when processing to that point as P k Calculate P using the following formula k :

[0025]

[0026] Beneficial technical effects brought about by the present invention:

[0027] Compared with the existing technology, the present invention combines droplet injection with laser, which can avoid the deformation, cracking and other problems caused by the extremely high cooling rate of materials in traditional laser additive manufacturing, and can also avoid the problem of poor droplet bonding in traditional droplet injection. Compared with the use of a single-beam paraxial laser, the present invention avoids the directionality of the processing process and improves the uniformity of component performance by integrating multiple paraxial lasers in a circular manner, and plans the distribution of the total laser power among multiple laser units according to the processing path. While obtaining a good interlayer bonding effect, more heat is input near the adjacent deposited paths to ensure a good inter-path bonding effect, thereby obtaining more outstanding mechanical properties. The role of the laser is only to slow down the heat dissipation of the deposited droplets and the surrounding areas, so the required laser power is relatively small, and the equipment cost increase brought by the laser light source is also relatively controllable. Since the water hammer on-demand injection device is small in size, the volume of the entire device can be controlled after integrating the coaxial laser. In summary, the present invention has a high application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of a water hammer type on-demand jetting-laser coaxial composite additive device in the present invention;

[0029] Figure 2 Schematic diagram of a laser power distribution planning method in a water hammer jet-on-demand-laser coaxial composite additive method according to the present invention;

[0030] Among them, 1 - water hammer on-demand injection device; 2 - ring-shaped laser light source; 3 - substrate; 4 - droplet; 5 - deposited component; 51 - the deposited path adjacent to the deposition path where point O is located in this layer; 52 - the deposition path where point O is currently planned; 6 - laser spot; 7 - nozzle; 8 - actuator; 9 - heating element; 10 - molten metal; DETAILED DESCRIPTION

[0031] The specific implementation of the present invention will be further described below with reference to specific embodiments:

[0032] A water hammer type on-demand jet-laser coaxial composite additive device, such as Figure 1 As shown, it includes a water hammer type on-demand injection device 1, a ring-type laser light source 2, a control unit and a base plate 3;

[0033] The water hammer type on-demand injection device 1 is used to melt the metal and realize on-demand injection of the molten droplets 4 by utilizing the water hammer pressure wave generated when the fluid velocity suddenly changes;

[0034] The annular laser light source 2 is composed of at least three laser units distributed symmetrically around the circumference, with the axis of symmetry being the injection axis of the water hammer type on-demand injection device 1. The lasers emitted by the multiple laser units are focused at a certain distance below the nozzle.

[0035] The substrate 3 is located below the nozzle and is capable of three-dimensional translation;

[0036] The control unit is used to synchronously control the on-demand injection of the water hammer type on-demand injection device 1 and the movement of the substrate 3, and independently control the light output and power of each laser unit.

[0037] Specifically, the water hammer type on-demand injection device 1 includes a nozzle 7, an actuator 8 and a heating element 9. The upper end of the nozzle 7 is connected to the actuator 8, and a nozzle hole is opened at the bottom end. The heating element 9 can melt the metal in the nozzle 7 into molten metal 10. When the actuator 8 drives the nozzle 7 to reciprocate along the axis with a micron-level stroke, the water hammer pressure wave caused by the sudden change of fluid velocity near the nozzle hole can cause the molten metal 10 to produce an on-demand injection, generating a molten droplet 4.

[0038] The actuating element 8 may be any device that can drive the nozzle to achieve micron-level reciprocating movement; the heating element 9 may be an electromagnetic induction heating system.

[0039] Specifically, the annular laser light source 2 is fixed to the lower end of the nozzle through a fixing frame, and multiple laser units are symmetrically distributed around the nozzle. The annular laser light source 2 uses continuous laser or pulsed laser. When pulsed laser is used, the laser power is adjusted by adjusting the duty cycle of the pulse.

[0040] A water hammer type on-demand jetting-laser coaxial composite additive method, using the water hammer type on-demand jetting-laser coaxial composite additive device as described above, performs additive manufacturing processing through the following steps:

[0041] Step 1: The control unit reads the 3D model of the component to be processed and performs processing path planning and laser power distribution planning. The processing path planning is to divide the component to be processed into multiple layers for layered processing, and each layer is divided into multiple deposition paths;

[0042] Step 2: The control unit adjusts the height of the substrate in the vertical direction so that the laser focus of the annular laser light source 2 is located on the upper surface of the substrate. If the first layer is to be deposited, the substrate is the substrate; otherwise, the substrate is the deposited component.

[0043] Step 3: The control unit synchronously controls the on-demand injection of the water hammer on-demand injection device 1 and the horizontal movement of the substrate 3 according to the processing path planned in step 1. Based on the laser power distribution planning result in step 1, the control unit turns on the circular laser light source 2 and adjusts the power of each laser unit to heat the molten droplet 4 currently deposited on the upper surface of the component and the deposited component 5 nearby, so as to achieve good interlayer bonding and inter-pass bonding within the same layer.

[0044] Step 4: Repeat steps 2 and 3 to complete the manufacturing of the component layer by layer.

[0045] Laser power allocation planning is performed through the following sub-steps:

[0046] Step 11: Set the interlayer laser power P layer and inter-channel laser power P pass The interlayer laser power is set according to the droplet temperature, droplet size, and deposition speed. The lower the droplet temperature, the larger the droplet, and the faster the deposition speed, the greater the required interlayer laser power. The interpass laser power should be smaller than the interlayer laser power.

[0047] Step 12: Figure 2 As shown, according to the processing path planning, the processing path is discretized into a series of points, and the laser power is calculated point by point. The currently planned point is recorded as O, which is the center point of multiple laser units. An empty set S is established. If the deposition path 52 where the currently planned point O is located is the first deposition path in the layer, then jump directly to step 13. Otherwise, the deposition path of the deposition path 51 adjacent to the deposition path where point O is located in the layer is recorded as L, and the normal line from point O to L is recorded as The direction is from O to L; the total number of laser units in the annular laser light source is N, and the center point of the laser spot 6 irradiated by each laser unit on the upper surface of the substrate is C k ,k=1,2,…,N;calculate each vector and The angle α k , if α k ≤90°, then α k The corresponding k is added to the set S;

[0048] Step 13: Let the power of the kth laser unit be P k Calculate P using the following formula k :

[0049]

[0050] The effect achieved by the above formula is to set the interlayer laser power P layer Evenly distribute it to each laser unit to achieve overall heating of the area where the droplet 4 is deposited, ensuring good interlayer bonding. At the same time, since the droplet 4 dissipates heat faster near the adjacent deposited track, the inter-track laser power P is set. pass Weighted allocation is made to the laser units corresponding to several light spots that are closer to the adjacent deposited tracks to achieve additional heating of the area close to the deposited tracks and ensure good inter-track bonding.

[0051] Example 1

[0052] The metal material used in additive manufacturing is tin, which has a melting point of about 230°C. The tin in the nozzle is heated to about 300°C using a heating element. The water hammer on-demand injection device can produce droplets with a diameter of about 200μm. The injection frequency is 100Hz. The movement speed of the substrate along the deposition path during the deposition process is set to 15mm / s. The circular laser light source consists of 4 laser units evenly arranged along the circumference. Each laser unit is a pulsed light source with an output power amplitude of 5W. Set the interlayer laser power P layer =8W, inter-channel laser power P pass =3W. The spot distribution and deposition direction generated by the laser unit are as follows Figure 2 As shown, when processing to point O, the deposition path L of the adjacent deposited channel passes through the normal line of O and and The angles are all less than 90°, α1 = 30°, and α4 = 60°. The calculated laser powers for the four laser units are P1 = 3.9W, P2 = 2W, P3 = 2W, and P4 = 3.1W. Based on this, the duty cycles of the four laser units are adjusted to 78%, 40%, 40%, and 62%, respectively. Droplet ejection is synchronized with substrate motion, and the deposition process continues.

[0053] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the scope of protection of the present invention.

Claims

1. A water hammer type on-demand jetting-laser coaxial composite additive device, characterized in that: It includes a water hammer type on-demand injection device, a ring-type laser light source, a control unit and a base plate; The water hammer type on-demand injection device is used to melt the metal and realize on-demand injection of molten droplets by utilizing the water hammer pressure wave generated when the fluid velocity changes suddenly; The annular laser light source is composed of at least three laser units distributed symmetrically around the circumference, the axis of symmetry being the injection axis of the water hammer type on-demand injection device, and the lasers emitted by the multiple laser units are focused at a certain distance below the spray hole; The substrate is located below the spray hole and can perform three-dimensional translation; The control unit is used to synchronously control the on-demand injection of the water hammer type on-demand injection device and the movement of the substrate, and independently control the light output and power of each laser unit.

2. A water hammer type on-demand jetting-laser coaxial composite additive device according to claim 1, characterized in that: The water hammer type on-demand injection device includes a nozzle, an actuating element and a heating element. The upper end of the nozzle is connected to the actuating element, and a nozzle hole is opened at the bottom end. The heating element can melt the metal in the nozzle. When the actuating element drives the nozzle to reciprocate along the axis with a micron-level stroke, the water hammer pressure wave caused by the sudden change of fluid velocity near the nozzle hole can cause the molten metal to produce an on-demand injection.

3. The water hammer type on-demand jetting-laser coaxial composite additive device according to claim 1, characterized in that: The annular laser light source adopts continuous laser or pulse laser. When pulse laser is adopted, the laser power is adjusted by adjusting the duty cycle of the pulse.

4. A water hammer type on-demand jetting-laser coaxial composite additive method, characterized in that: Using a water hammer type on-demand jetting-laser coaxial composite additive device as described in any one of claims 1 to 3, additive manufacturing is performed through the following steps: Step 1: The control unit reads the three-dimensional model of the component to be processed, and performs processing path planning and laser power distribution planning. The processing path planning is to divide the component to be processed into multi-layer components for layered processing; Step 2: The control unit adjusts the height of the substrate in the vertical direction so that the laser focus of the annular laser light source is located on the upper surface of the substrate. If the first layer is to be deposited, the substrate is the substrate, otherwise the substrate is the deposited component; Step 3: The control unit synchronously controls the on-demand injection of the water hammer on-demand injection device and the movement of the substrate in the horizontal plane according to the processing path planned in step 1, and according to the laser power distribution planning result in step 1, turns on the annular laser light source and adjusts the power of each laser unit to heat the molten droplets currently deposited on the upper surface of the substrate and the surrounding area, so as to achieve good interlayer bonding and inter-channel bonding within the same layer; Step 4: Repeat steps 2 and 3 to complete the manufacturing of the component layer by layer.

5. A water hammer type on-demand jetting-laser coaxial composite additive method according to claim 4, characterized in that: In step 1, laser power allocation planning is performed through the following sub-steps: Step 11: Set the interlayer laser power P layer and inter-channel laser power P pass , the inter-layer laser power should be greater than the inter-channel laser power; Step 12: According to the processing path planning, the processing path is discretized into a series of points, and the laser power is calculated point by point. The currently planned point is recorded as O, and an empty set S is established. If the deposition path where point O is located is the first deposition path in the layer, jump directly to step 13. Otherwise, the deposition path of the deposition path adjacent to the deposition path where point O is located in the layer is recorded as L, and the normal line from point O to L is recorded as The direction is from O to L; the total number of laser units in the annular laser light source is N, and the center point of the laser spot irradiated by each laser unit on the upper surface of the substrate is C k , k = 1, 2, ..., N, calculate each vector and The angle α k , if α k ≤90°, then add k to the set S; Step 13: For each point on the processing path, record the power of the kth laser unit when processing to that point as P k , calculate P by the following formula k :

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