阅读说明：本技术 减少激光选区熔化成形件内部孔隙缺陷的方法和装置 (Method and device for reducing internal pore defects of selective laser melting formed part ) 是由 谢德巧 于 2021-06-15 设计创作，主要内容包括：本发明公开了一种利用图形识别与铣削技术,减少激光选区熔化成形金属零件内部孔隙缺陷的方法和装置。首先利用热成像仪模块识别激光选区熔化过程中某一层温度异常和突变区域,结合该层冷却后的表面形貌,判断孔隙缺陷出现的位置与区域。随后利用路径规划软件规划出铣刀的铣削路径,将该层出现孔隙缺陷的区域材料进行去除。接着再用刮刀铺一次粉,已被铣削去除的区域可利用激光再次熔化。在激光选区熔化逐层累加的过程中,每一层均可快速寻找、修复孔隙缺陷,实现了每一层成形质量的稳定控制。本发明可以有效控制每一层的缺陷,最终减少激光选区熔化成形零件的孔隙缺陷,显著提升其力学性能。(The invention discloses a method and a device for reducing internal pore defects of a metal part formed by selective laser melting by utilizing a pattern recognition and milling technology. Firstly, a thermal imager module is utilized to identify a certain layer of abnormal temperature and abrupt change area in the selective laser melting process, and the position and area of the pore defect are judged by combining the surface appearance of the layer after cooling. And planning a milling path of the milling cutter by using path planning software, and removing the material of the region with the pore defect. The powder is then spread once more with a doctor blade and the milled away areas can be remelted with a laser. In the process of melting and accumulating layer by layer in the selective laser area, the pore defects can be quickly found and repaired for each layer, and the forming quality of each layer is stably controlled. The invention can effectively control the defect of each layer, finally reduce the pore defect of the part formed by selective laser melting and obviously improve the mechanical property of the part.)

1. The device for reducing the internal pore defects of the selective laser melting formed part is characterized by comprising a thermal imager module (4), a milling module (1), a scanning galvanometer (2), a laser (3), a scraper (6), a forming cavity (7), a forming cylinder (8) and a powder feeding cylinder (9), wherein the forming cylinder (8) and the powder feeding cylinder (9) are respectively arranged at the bottom (7) of the forming cavity, and metal powder in the powder feeding cylinder (9) is scraped into the forming cylinder (8) by the scraper (6) and is laid flat; the laser (3) is connected with the scanning galvanometer (2), the scanning galvanometer (2) is arranged on the forming cavity (7), and the scanning galvanometer (2) is aligned with the forming piece (5) in the forming cylinder (8); the thermal imager module (4) is arranged at the top of the forming cavity (7); the milling module (1) is arranged inside the forming cavity (7) and is connected with the forming cavity.

2. The apparatus according to claim 1, wherein the thermal imaging module (4) identifies the temperature field during the selective laser melting and forming process and the surface roughness after cooling, and if the abnormal temperature region exceeding the preset range overlaps with the region where the surface roughness after cooling exceeds the set first threshold or the distance between the two is less than the second threshold, the abnormal temperature region is determined to be a region where a void defect occurs.

3. The apparatus according to claim 1, characterized in that the milling module (1) comprises a robot/XYZ-triaxial guide, a milling cutter, which is moved to the area of the pore defect by means of the robot/XYZ-triaxial guide.

4. The apparatus of claim 3, wherein the lower end surface of the milling cutter is 20 to 50 μm lower than the selective laser melting surface during milling.

5. A method for reducing the internal porosity defects of a selective laser melting forming piece based on the device of any one of claims 1 to 4, characterized by comprising the following specific steps:

1) scraping metal powder in a powder feeding cylinder (9) into a forming cylinder (8) by using a scraper and paving the metal powder, opening a laser (3), and melting a target area by laser emitted by the laser (3) after scanning a galvanometer (2);

2) identifying the temperature field of a certain layer in the selective laser melting process by using a thermal imager module (4), and recording an abnormal temperature area exceeding a preset range;

3) turning off the laser (3), identifying the surface roughness after cooling by using a thermal imager module (4), and if the abnormal temperature area is overlapped with the area of which the surface roughness exceeds a set first threshold value after cooling or the distance between the abnormal temperature area and the area is smaller than a set second threshold value, determining that the abnormal temperature area is an area with a pore defect;

4) and planning a milling path of the milling cutter by using path planning software, and removing the material in the region where the layer of the hole defects are located.

5) Spreading powder again by using a scraper, opening the laser (3), and carrying out laser scanning melting on the milled and removed area in the step 4);

6) and (3) turning off the laser (3), and returning to the step 1) until the formed piece is printed out.

Technical Field

The invention relates to a method and a device for reducing internal pore defects of a selective laser melting forming part based on an image recognition and milling technology, in particular to a method and a device for reducing internal pore defects of a selective laser melting forming metal part based on thermal imager module recognition and milling module repair, and belongs to the field of laser additive manufacturing.

Background

The Selective Laser Melting (SLM) technology is one of the main processes currently used for metal additive manufacturing, and due to the advantages of the Selective Laser Melting (SLM) technology in the aspects of forming complex structures, part precision, surface quality and the like, the Selective Laser Melting (SLM) technology is widely applied to multiple fields of aerospace complex parts, personalized biomedical devices and the like.

However, parts manufactured by the selective laser melting additive manufacturing technology often have internal porosity defects, which can reduce the mechanical properties, especially the fatigue strength. There are many domestic and foreign researches on the problem of the pores in the SLM, and the scholars generally believe that the pores in the SLM influence the mechanical properties of parts, especially fatigue strength. Therefore, to print high performance SLM structures, it is desirable to reduce void defects, especially large voids with dimensions above 200 microns.

At present, the method for eliminating the porosity defect of the SLM forming part mainly comprises the following hot isostatic pressing treatment, hot isostatic pressing equipment is expensive, a large amount of energy is consumed, the microstructure is easy to coarsen, and the mechanical property of the forming part is reduced.

Disclosure of Invention

The invention provides a method and a device for reducing internal pore defects of a selective laser melting forming part based on image recognition and milling technologies, which aims to solve the problems and provide an idea of online identification and repair of pore defects.

The invention adopts the following technical scheme for solving the technical problems:

the device for reducing the internal pore defects of the selective laser melting forming part based on the image recognition and milling technology comprises a thermal imager module, a milling module, a scanning galvanometer, a laser, a scraper, a forming cavity, a forming cylinder and a powder feeding cylinder, wherein the forming cylinder and the powder feeding cylinder are respectively arranged at the bottom of the forming cavity, and metal powder in the powder feeding cylinder is scraped into the forming cylinder by the scraper and is paved; the laser is connected with the scanning galvanometer, the scanning galvanometer is arranged on the forming cavity, and the scanning galvanometer is aligned to a forming piece in the forming cylinder; the thermal imager module is arranged at the top of the forming cavity; the milling module is arranged inside the forming cavity and connected with the forming cavity.

Further, a temperature field in the selective laser melting forming process and the cooled surface roughness are identified through a thermal imager module, and if an abnormal temperature area exceeding a preset range is overlapped with an area, the cooled surface roughness of which exceeds a set first threshold, or the distance between the abnormal temperature area and the area is smaller than a second threshold (2mm), the abnormal temperature area is judged to be an area with a pore defect.

Further, the milling module comprises a manipulator/XYZ three-axis guide rail and a milling cutter, and the milling cutter is moved to the area where the pore defects are located through the manipulator/XYZ three-axis guide rail.

Furthermore, during milling, the lower end surface of the milling cutter is 20-50 microns lower than the melting molding surface of the laser selective area.

The method for reducing the internal pore defects of the selective laser melting forming part based on the device comprises the following specific steps:

1) scraping metal powder in the powder feeding cylinder into the forming cylinder by using a scraper, paving the metal powder, turning on a laser, and melting a target area by laser emitted by the laser after scanning a vibrating mirror;

2) identifying the temperature field of a certain layer in the selective laser melting process by using a thermal imager module, and recording an abnormal temperature area exceeding a preset range;

3) closing the laser, identifying the surface roughness after cooling by using a thermal imager module, and if the abnormal temperature area is overlapped with the area of which the surface roughness exceeds a set first threshold value after cooling or the distance between the abnormal temperature area and the area is less than a set second threshold value, determining that the abnormal temperature area is an area with a pore defect;

4) and planning a milling path of the milling cutter by using path planning software, and removing the material in the region where the layer of the hole defects are located.

5) Spreading powder again by using a scraper, opening a laser, and carrying out laser scanning melting on the milled and removed area in the step 4);

6) and turning off the laser, and returning to the step 1) until the formed piece is printed.

Compared with the prior art, the invention adopting the technical scheme has the following technical effects: the position of the pore defect is judged through a pattern recognition technology, the pore defect is removed on line through a milling technology, and then the area is repaired through laser, so that the defect of each layer can be repaired, and the method has the beneficial effects of improving the mechanical property and the forming quality stability of the metal additive manufacturing part.

Drawings

FIG. 1 is a schematic view of an apparatus for reducing internal void defects in a selectively laser-melted formed part based on image recognition and milling;

FIG. 2 is a schematic diagram of a control method of an apparatus for reducing internal void defects of a laser selective melting formed part based on image recognition and milling technology;

FIG. 3 is an example of void defect identification (region A), milling (region B), re-powdering, and laser melting (region C);

the device comprises a milling module 1, a scanning galvanometer 2, a laser 3, a thermal imager module 4, a forming piece 5, a scraper 6, a forming cavity 7, a forming cylinder 8 and a powder feeding cylinder 9.

Detailed Description

The technical scheme of the invention is further explained by combining the drawings and the specific embodiments:

a device for reducing internal pore defects of a selective laser melting forming part based on image recognition and milling technology comprises a thermal imager module, a milling module, a scanning galvanometer, a laser, a scraper, a forming cavity, a forming cylinder and a powder feeding cylinder, wherein the forming cylinder and the powder feeding cylinder are respectively arranged at the bottom of the forming cavity, metal powder in the powder feeding cylinder is scraped into the forming cylinder by the scraper and is paved, the laser is connected with the scanning galvanometer, the scanning galvanometer is arranged on the forming cavity, the scanning galvanometer is aligned to forming parts in the forming cylinder, the thermal imager module is arranged at the upper part of the forming cavity, and the milling module is arranged in the forming cavity and is connected with the forming cavity.

The thermal imaging system module can identify a temperature field in the selective laser melting forming process and the cooled surface roughness, and if an abnormal temperature area exceeding a preset range is overlapped or close to an area with the cooled surface roughness exceeding a set threshold (the distance between the abnormal temperature area and the area is less than 2mm), the abnormal temperature area can be judged to be an area with a pore defect.

The milling module comprises a manipulator (or an XYZ three-axis guide rail) and a milling cutter, and the manipulator (or the XYZ three-axis guide rail) can move the milling cutter to the area where the pore defect is located. During milling, the lower end surface of the milling cutter is 20-50 microns lower than the melting molding surface of the laser selective area.

As shown in fig. 2, the control method of the apparatus specifically includes: firstly, under the control of a master control module, the device executes conventional SLM forming; secondly, identifying the temperature field of the selective laser melting and forming process and the surface roughness after cooling by using an infrared thermal imager; and thirdly, after the analysis of the data analysis system, if an area with a pore defect exists, the device performs repair under the control of the master control module so as to reduce the defect of the internal gap.

The method for reducing the internal pore defects of the metal part based on the device comprises the following specific steps:

1) scraping metal powder in the powder feeding cylinder into the forming cylinder by using a scraper, paving the metal powder, turning on a laser, and melting a target area by laser emitted by the laser after scanning a vibrating mirror;

2) identifying the temperature field of a certain layer in the selective laser melting process by using a thermal imager module, and recording an abnormal temperature area exceeding a preset range;

3) closing the laser, identifying the surface roughness after cooling by using a thermal imager module, and if the abnormal temperature area is overlapped with the area of which the surface roughness exceeds a set first threshold value after cooling or the distance between the abnormal temperature area and the area is less than a set second threshold value, determining that the abnormal temperature area is an area with a pore defect;

4) and planning a milling path of the milling cutter by using path planning software, and removing the material in the region where the layer of the hole defects are located.

5) Spreading powder again by using a scraper, opening a laser, and carrying out laser scanning melting on the milled and removed area in the step 4);

6) and turning off the laser, and returning to the step 1) until the formed piece is printed.

Example 1: manufacture of 316L stainless steel parts

A method for reducing internal pore defects of a selective laser melting forming piece based on image recognition and milling technology comprises the following steps:

step 1, fixing a thermal imager module on the upper part of a forming cavity, and fixing a milling module in the forming cavity;

step 2, scraping the metal powder in the powder feeding cylinder into the forming cylinder by using a scraper and paving the metal powder; the used material is 316L stainless steel, the grain diameter is 15-53 microns, and the layer thickness is 30 microns;

step 3, turning on a laser switch, melting a target area, wherein the laser power is 180W, the scanning speed is 1m/s, the lap joint rate is 40%, and identifying the temperature abnormal area of the layer in the selective laser melting process by using a thermal imager module;

step 4, closing a laser switch, identifying the surface roughness after cooling in the selective laser melting process by using a thermal imager module, and judging that a formed part has a pore defect if a temperature abnormal area in the processing process is close to or overlapped with an area with larger surface roughness after processing;

step 5, moving the milling cutter to a region where the pore defects are located by using a robot (or an XYZ three-axis guide rail), wherein the milling region can be properly expanded into a regular rectangle or circle and the like (as shown in FIG. 3, a region B and a region C are regions for powder re-spreading and laser melting), and the milling depth is 30 microns of the printing layer thickness;

step 6, after milling, sucking away the cutting chips by using a dust collector, then putting the chips on a powder transferring cylinder, spreading powder by using a scraper, and filling metal powder into the milled area;

step 7, turning on a laser switch, and melting the milled and powder-spread area;

step 8, closing a laser switch;

and (5) repeating the steps 2-8 for multiple times, and finally printing a formed piece with less internal pore defects.

Example 2: production of Ti6Al4V parts

A method for reducing internal pore defects of a selective laser melting forming piece based on image recognition and milling technology comprises the following steps:

step 1, fixing a thermal imager module on the upper part of a forming cavity, and fixing a milling module in the forming cavity;

step 2, scraping the metal powder in the powder feeding cylinder into the forming cylinder by using a scraper and paving the metal powder; the used material is Ti6Al4V titanium alloy, the grain diameter is 15-53 microns, and the layer thickness is 30 microns;

step 3, turning on a laser switch, melting a target area, wherein the laser power is 130W, the scanning speed is 1m/s, the lap joint rate is 40%, and identifying the temperature abnormal area of the layer in the selective laser melting process by using a thermal imager module;

step 4, closing a laser switch, identifying the surface roughness after cooling in the selective laser melting process by using a thermal imager module, and judging that a formed part has a pore defect if a temperature abnormal area in the processing process is close to or overlapped with an area with larger surface roughness after processing;

step 5, moving the milling cutter to a region where the pore defects are located by using a robot (or an XYZ three-axis guide rail), wherein the milling region can be properly expanded into a regular rectangle or circle and the like, and the milling depth is 30 microns of the printing layer thickness;

step 6, after milling, sucking away the cutting chips by using a dust collector, then putting the chips on a powder transferring cylinder, spreading powder by using a scraper, and filling metal powder into the milled area;

step 7, turning on a laser switch, and melting the milled and powder-spread area;

step 8, closing a laser switch;

and (5) repeating the steps 2-8 for multiple times, and finally printing a formed piece with less internal pore defects.

The method comprises the steps of firstly identifying a certain layer of abnormal temperature and abrupt change region in the selective laser melting process by using a thermal imager module, and judging the position and the region of a pore defect by combining the surface appearance of the layer after cooling. And planning a milling path of the milling cutter by using path planning software, and removing the material of the region with the pore defect. The powder is then spread once more with a doctor blade and the milled away areas can be remelted with a laser. In the process of melting and accumulating layer by layer in the selective laser area, the pore defects can be quickly found and repaired for each layer, and the forming quality of each layer is stably controlled. The invention can effectively control the defect of each layer, finally reduce the pore defect of the part formed by selective laser melting and obviously improve the mechanical property of the part.

It should be noted that the above description of the embodiments is only for the purpose of assisting understanding of the method of the present application and the core idea thereof, and that those skilled in the art can make several improvements and modifications to the present application without departing from the principle of the present application, and these improvements and modifications are also within the protection scope of the claims of the present application.