Additive manufacturing method for synchronously carrying out powder bed powder laying and laser melting preheating

Abstract

The invention belongs to the technical field of additive manufacturing, and particularly relates to an additive manufacturing method for synchronously carrying out powder bed powder laying and laser melting preheating, which comprises the following steps: S1, after a current layer is formed, a powder laying mechanism starts to lay powder; s2, scanning powder in an unshielded area on the powder bed in a grating manner by adopting a low-power or large-spot laser; s3, dividing the powder in the shielding area into a marched side area and a non-marched side area of the powder spreading mechanism; s4, along with operation of the powder spreading mechanism, the areas change in real time; s5, after powder laying is finished, the whole powder of the powder bed continues to be scanned through the small-power laser grating type; and S6, repeating the steps S1 to S5. The powder on the powder bed is preheated in real time through low-power laser, the heating device has the advantages of being high in heating speed, large in heating area and the like, the defect that the transmission efficiency of bottom plate preheating and heat radiation preheating is low is overcome, and the defect that the temperature of the powder bed is obviously reduced due to the fact that the powder laying process of large-size parts is too long is overcome.

Description

Technical Field

[0001] The present invention belongs to the technical field of additive manufacturing, and in particular relates to an additive manufacturing method in which powder bed laying and laser melting preheating are performed simultaneously. Background Art

[0002] Powder bed laser melting technology is a 3D printing process that selectively melts powder through laser. This technology can directly form parts by melting powder layer by layer. It has the characteristics of high complexity of formed parts and fast forming speed. It has important applications in the fields of aviation, aerospace, automobiles, etc. It is one of the ideal forming methods for precision and complex metal parts.

[0003] However, in the powder bed laser melting process of large parts, the scraper spreads the powder for a long time, causing the temperature of the forming area to drop quickly, and the temperature difference between different areas is large, resulting in large thermal stress inside the formed parts, greatly increasing the risk of deformation and cracking of the formed parts. At the same time, for high-strength materials that are sensitive to thermal cracks, the rapid cooling and heating characteristics brought about by laser heating also increase the risk of part cracking.

[0004] Among them, preheating all the powder on the powder bed is an effective method to reduce the temperature difference and slow down the cooling rate, which can greatly improve the quality of the formed parts.

[0005] Currently, the methods for preheating the powder bed mainly include the following:

[0006] First, as described in the patent applications with publication numbers CN113618084A and CN107552789A, the projection preheating method described in the CN113618084A patent application has a preheating area that changes with the change of the layer geometry (actual part area), and the temperature difference between the layer area and the surrounding powder still exists, and the thermal stress of the formed part still exists; the method described in the CN107552789A patent application installs a foldable radiation heating source on the upper part of the powder bed, but the method of preheating the powder bed by thermal radiation has a low heating efficiency, and there is a large amount of loss of heat emitted by the heat source when it reaches the powder bed.

[0007] Second, as described in the patent applications with publication numbers CN115533126A, CN108380877B, CN108500270B and CN117245101A, the method described in the patent application CN115533126A places a dot matrix fiber laser head on the two side walls of the laser melting forming cavity perpendicular to the movement direction of the powder spreading scraper, and emits the powder obliquely to the forming area. The irradiation distances of different laser heads are inconsistent, resulting in uneven preheating of the powder; the method described in the patent application CN108380877B uses two laser heads. The laser preheats the laid powder with a low power laser and scans and forms it with a high power laser, but the preheating of the powder during the laying process is not achieved; the method described in the CN117245101A patent application uses an electron beam to directly preheat the powder, the preheating time is 2 to 4 hours, and the number of scans per layer is 15 to 100 times, the forming time is long, and the efficiency is low; the method described in the CN108500270B patent application uses a laser beam to preheat and scan the laid powder to avoid "blowing powder", but the preheating while laying is not achieved. The laser beam in this patent application is emitted from directly above the powder bed, which not only has good preheating uniformity, but also adopts preheating while laying, and has high heating efficiency.

[0008] Third, as described in the patent application with publication number CN107812945A, a heater is installed on the outer wall of the material box to preheat the powder. Although this method can increase the powder temperature to a certain extent, there are problems such as the powder in the powder box easily forming an "arch bridge" and causing powder feeding blockage, uneven temperature of the outer layer and inner layer of the powder box, and fast heat dissipation of the powder during the powder spreading process.

[0009] Fourth, as described in the patent applications with publication numbers CN217290417U and CN204639131U, a large number of heating rods or electromagnetic induction heating are installed around or at the bottom of the forming cylinder to achieve the purpose of preheating the powder and parts. However, with this heating method, as the height of the formed part increases, the heat from the bottom plate is difficult to transfer to the powder layer to be formed and the surface of the part; and due to the flow of inert or neutral gas in the forming chamber and the requirement to ensure that the piston movement of the forming cylinder does not "get stuck", the heating temperature is limited and the forming of thermal crack-sensitive materials and large-sized parts cannot be guaranteed.

[0010] It can be seen that the current preheating methods of powder beds include radiation preheating, powder box preheating and base plate preheating, but the above preheating methods cannot meet the forming requirements of large-size parts and thermal crack-sensitive materials. The overall forming time is prolonged and the production efficiency is low, which has certain limitations in actual production.

[0011] Therefore, how to achieve convenient and efficient overall preheating of the powder bed and how to reduce the internal stress and deformation of parts have become urgent issues that need to be solved in powder bed laser melting technology. Summary of the invention

[0012] In order to solve the problems existing in the above-mentioned prior art, the present invention provides an additive manufacturing method for simultaneously performing powder bed laying and laser melting preheating, and uses a low-power laser to preheat the powder on the powder bed in real time. It has the characteristics of fast heating speed and large heating area, which avoids the shortcomings of low base plate preheating and heat radiation preheating transfer efficiency, and avoids the shortcoming of a significant drop in powder bed temperature caused by a long powder laying process for large-sized parts. It can provide a good thermal environment for laser melting forming of large-sized parts and thermal crack sensitive materials.

[0013] The specific technical solution adopted by the present invention is:

[0014] An additive manufacturing method for simultaneously performing powder bed laying and laser melting preheating comprises the following steps:

[0015] S1. After the current layer is formed, the powder spreading mechanism starts spreading powder. After the position sensor senses the position of the powder spreading mechanism, the powder on the powder bed is divided into powder in the blocked area and powder in the unblocked area.

[0016] S2, using low-power or large-spot laser raster scanning to preheat the powder in the unblocked area of ​​the powder bed;

[0017] S3, dividing the powder in the blocked area into the area on the side where the powder spreading mechanism has moved and the area on the side where the powder spreading mechanism has not moved, the laser scanning area on the area on the side where the powder has moved is the actual area, and the area on the side where the powder has not moved is the area enclosed by reducing a certain travel distance Δ, so as to avoid interference between the powder spreading mechanism and the laser;

[0018] S4. As the powder spreading mechanism operates, the above areas change in real time;

[0019] S5. After the powder is spread, continue to use a low-power laser to raster scan the entire powder bed. When the powder temperature reaches the forming temperature setting value, forming begins;

[0020] S6, repeating the above steps S1 to S5 until the additive manufacturing of the entire part is completed;

[0021] in

[0022] Where S is the powder bed area in mm 2 ;

[0023] x3 is the width of the powder spreading mechanism, in mm;

[0024] y is the width of the powder bed, in mm;

[0025] t is time, in seconds;

[0026] v1 and v2 are the scanning areas per unit time of the laser scanning heads on both sides of the powder spreading mechanism, respectively, in mm / s.

[0027] The laser raster scanning includes any one of X-direction scanning, Y-direction scanning, grid line scanning, layered interlaced scanning and zigzag scanning.

[0028] The particle size of the powder is 10 to 105 μm.

[0029] The temperature of the powder reaches 100-500° C. after preheating.

[0030] The temperature setting value of each layer of powder is set to increase layer by layer from top to bottom, and the increasing temperature value is 0.1-0.2°C.

[0031] The beneficial effects of the present invention are:

[0032] 1. This patent proposes a method of preheating the powder bed while spreading the powder, using a low-power laser to preheat the powder on the powder bed in real time. It has the characteristics of fast heating speed and large heating area. It avoids the shortcomings of low transfer efficiency of base plate preheating and thermal radiation preheating, and avoids the disadvantage of a significant drop in powder bed temperature caused by a long powder spreading process for large-size parts. It can provide a good thermal environment for laser melting forming of large-size parts and thermal crack-sensitive materials.

[0033] 2. The preheating value of each layer of powder in the present invention is set with a temperature difference. The preheating temperature of the powder from the bottom layer to the top layer is a step-by-step increase in temperature to compensate for the heat loss of each layer of powder, ensuring that after all the powders are laid and preheated, the temperature of each layer of powder is basically the same, thereby ensuring the quality of powder bed laser melting forming. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of the process of the present invention;

[0035] Figure 2 It is a schematic diagram of the temperature setting value temperature measuring device;

[0036] Figure 3 It is a schematic diagram of real-time preheating of laser in a powder-spreading additive manufacturing device applicable to the present invention;

[0037] Figure 4 is the motion diagram of the travel distance △;

[0038] In the attached drawings, 1, positive electrode wire of thermocouple, 1', negative electrode wire of thermocouple, 2, forming cylinder, 3, lifting piston, 4, positive electrode wire of thermocouple, 4', negative electrode wire of thermocouple, 5, powder, 6, forming base plate, 7, powder spreading mechanism, A, unobstructed area, A', unobstructed area; B, obstructed area; X1y, traveling side area; X2y, non-traveling side area; X3y, obstructed area; △, traveling distance. DETAILED DESCRIPTION

[0039] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. 1. Specific embodiments

[0041] Specific embodiments, such as Figure 1 to Figure 4 As shown, the present invention provides an additive manufacturing method in which powder bed laying and laser melting preheating are performed simultaneously, comprising the following steps:

[0042] S1. After the current layer is formed, the powder spreading mechanism starts spreading powder. After the position sensor senses the position of the powder spreading mechanism, the powder on the powder bed is divided into powder in the blocked area and powder in the unblocked area.

[0043] S2, using low-power or large-spot laser raster scanning to preheat the powder in the unblocked area of ​​the powder bed;

[0044] S3, dividing the powder in the blocked area into the area on the side where the powder spreading mechanism has moved and the area on the side where the powder spreading mechanism has not moved, the laser scanning area on the area on the side where the powder has moved is the actual area, and the area on the side where the powder has not moved is the area enclosed by reducing a certain travel distance Δ, so as to avoid interference between the powder spreading mechanism and the laser;

[0045] S4. As the powder spreading mechanism operates, the above areas change in real time;

[0046] S5. After the powder is spread, continue to use a low-power laser to raster scan the entire powder bed. When the powder temperature reaches the forming temperature setting value, forming begins;

[0047] S6, repeating the above steps S1 to S5 until the additive manufacturing of the entire part is completed;

[0048] When the laser raster scanning mode is x-direction scanning,

[0049] Where S is the powder bed area in mm 2 ;

[0050] x3 is the width of the powder spreading mechanism, in mm;

[0051] y is the width of the powder bed, in mm;

[0052] t is time, in seconds;

[0053] v1 and v2 are the scanning areas per unit time of the laser scanning heads on both sides of the powder spreading mechanism, respectively, in mm / s.

[0054] The current preheating methods for powder beds include radiation preheating, powder box preheating, and base plate preheating. However, none of the above preheating methods can meet the forming requirements of large-sized parts and thermal crack-sensitive materials, and there are certain limitations in actual production. Although the preheating problem after powder laying can be solved, it will extend the overall forming time and reduce production efficiency. Therefore, how to achieve convenient and efficient overall preheating of the powder bed and how to reduce the internal stress and deformation of parts have become urgent problems to be solved in powder bed laser melting technology.

[0055] like Figure 3 , Figure 4 As shown, in the present invention, a low-power laser is used to preheat the powder on the powder bed in real time, which has the characteristics of fast heating speed and large heating area. It avoids the shortcomings of low transfer efficiency of base plate preheating and thermal radiation preheating, and avoids the disadvantage of a significant drop in powder bed temperature caused by a long powder spreading process of large-sized parts. It can provide a good thermal environment for laser melting forming of large-sized parts and thermal crack sensitive materials.

[0056] S and x3y in the formula are constants, so the distance Δ is only negatively correlated with the scanning speeds v1 and v2. Figure 4 As shown, S=X1y+X2y+x3y+△y.

[0057] The laser raster scanning includes any one of X-direction scanning, Y-direction scanning, grid line scanning, layered interlaced scanning and zigzag scanning.

[0058] The particle size of the powder is 10 to 105 μm. This specific embodiment takes AlSi10Mg powder with a particle size of 30 μm as an example, assuming that it is preheated to 120°C, and the laser process parameters for preheating it are: laser power 50W, scanning speed 1000 mm / s, and the setting of each parameter needs to be determined according to the particle size and thermal conductivity of the powder.

[0059] The temperature of the powder after preheating reaches 100-500° C., and the preheating temperature should not be too high to avoid spheroidization, sintering or melting.

[0060] The temperature preset value of each layer of powder is set to increase layer by layer from top to bottom, and the increasing temperature value is 0.1-0.2°C. Since each layer of powder requires a certain process and time to lay, this results in the bottom layer of powder constantly dissipating heat outward during the laying of the next layer of powder. After all the powders are laid and preheated, a temperature gradient will appear, and a temperature difference will appear between the bottom layer of powder and the top layer of powder, affecting the quality of laser melting forming. Therefore, a temperature difference is set, and the powder preheating temperature from the bottom to the top layer is an increasing temperature to compensate for the heat loss of each layer of powder, ensuring that the temperature of each layer of powder is basically the same after all the powders are laid and preheated.

Claims

1. An additive manufacturing method in which powder bed laying and laser melting preheating are performed simultaneously, characterized in that: The following steps are involved: S1. After the current layer is formed, the powder spreading mechanism starts spreading powder. After the position sensor senses the position of the powder spreading mechanism, the powder on the powder bed is divided into powder in the blocked area and powder in the unblocked area. S2, using low-power or large-spot laser raster scanning to preheat the powder in the unblocked area of ​​the powder bed; S3, dividing the powder in the blocked area into the area on the side where the powder spreading mechanism has moved and the area on the side where the powder spreading mechanism has not moved, the laser scanning area on the area on the side where the powder has moved is the actual area, and the area on the side where the powder has not moved is the area enclosed by reducing a certain travel distance Δ, so as to avoid interference between the powder spreading mechanism and the laser; S4. As the powder spreading mechanism operates, the above areas change in real time; S5. After the powder is spread, continue to use a low-power laser to raster scan the entire powder bed. When the powder temperature reaches the forming temperature setting value, forming begins; S6, repeating the above steps S1 to S5 until the additive manufacturing of the entire part is completed; in Where S is the powder bed area in mm 2 ; x3 is the width of the powder spreading mechanism, in mm; y is the width of the powder bed, in mm; t is time, in seconds; v1 and v2 are the scanning areas per unit time of the laser scanning heads on both sides of the powder spreading mechanism, respectively, in mm / s.

2. The additive manufacturing method of claim 1 wherein powder bed laying and laser melting preheating are performed simultaneously, characterized in that: The laser raster scanning includes any one of X-direction scanning, Y-direction scanning, grid line scanning, layered interlaced scanning and zigzag scanning.

3. The additive manufacturing method of claim 1 wherein powder bed laying and laser melting preheating are performed simultaneously, characterized in that: The particle size of the powder is 10 to 105 μm.

4. The additive manufacturing method of claim 1 wherein powder bed laying and laser melting preheating are performed simultaneously, characterized in that: The temperature of the powder reaches 100-500° C. after preheating.

5. The additive manufacturing method of claim 1 wherein powder bed laying and laser melting preheating are performed simultaneously, characterized in that: The temperature setting value of each layer of powder is set in a step-by-step manner from top to bottom, and the increasing temperature value is 0.1-0.2°C.

Images