CN115255399A - 3D printing device and method for eliminating printing defects by utilizing micro-area synchronous heat treatment - Google Patents

Abstract

The invention discloses a 3D printing device and a method for eliminating printing defects by utilizing micro-area synchronous heat treatment, wherein the 3D printing device comprises a 3D printing device body and an infrared halogen lamp; the infrared halogen lamp is arranged near a laser printing head of the 3D printing device body, and the infrared halogen lamp is used for heating the molten pool micro-area position which is melted by the laser in the early stage to the heat treatment temperature in the laser processing process so as to gradually cool the molten pool; the synergistic effect of high-energy laser point-type melting and low-energy infrared point-type heat treatment is realized by using the laser and the infrared light source as heat sources, and the point-type melting-solidification and point-type online infrared light source in-situ heat treatment are utilized to eliminate internal stress, avoid the accumulation of the internal stress and ensure the additive manufacturing quality.

Description

3D printing device and method for eliminating printing defects by utilizing micro-area synchronous heat treatment

Technical Field

The invention relates to a laser processing technology, in particular to a 3D printing device and a method for eliminating printing defects by utilizing micro-area synchronous heat treatment.

Background

The laser processing is a processing mode of utilizing the energy of light to reach high energy density on a focus after being focused by a lens and processing by the photo-thermal effect. The laser processing does not need tools, has high processing speed, small surface deformation and wide range of processable materials. The material is subjected to various processes such as drilling, cutting, scribing, welding, heat treatment, etc. with a laser beam. The laser processing belongs to non-contact processing, and the energy and the moving speed of the high-energy laser beam are adjustable, so that the aim of various processing can be fulfilled. The laser processing technology has the following unique advantages of (1) high laser processing efficiency and reliable quality; (2) by means of the characteristic of non-contact processing, a closed container or a severe environment and places which are difficult to access by other people can be processed through the transparent medium, no cutter is abraded, and no cutting force acts on a workpiece; (4) the processing method can be used for processing various metals and non-metals, and particularly can be used for processing materials with high hardness, high brittleness and high melting point; (5) the laser beam is easy to guide and focus to realize the change of all directions, and is very easy to be matched with a numerical control system to process a complex workpiece; (6) the laser beam has high energy density and high processing speed, is processed locally, and has no or little influence on non-laser irradiation parts; (7) the divergence angle of the laser beam can be less than 1 milliarc, the diameter of a light spot can be as small as a micron magnitude, the acting time can be as short as a nanosecond and a picosecond, and meanwhile, the continuous output power of a high-power laser can reach a kilowatt magnitude to a 10kW magnitude, so that the laser is suitable for precision micro-machining and large-scale material machining. With the continuous and deep research on laser processing technology, equipment and process, laser processing has a wider application prospect.

Laser processing has become one of the main ways of welding and 3D printing refractory metal materials due to the advantages of laser processing. However, due to the high melting point and the rapid heat conduction of the refractory metal material, the part undergoes long-term periodic severe heating and rapid cooling of a high-energy laser beam in the laser forming process, rapid solidification shrinkage of a moving molten pool under strong constraint of the pool bottom and accompanying short-time non-equilibrium cycle solid state phase change to generate large and extremely complex thermal stress, structural stress, mechanical constraint stress and strong non-steady interaction and stress concentration inside the part, so that the part is seriously deformed and cracked.

The basic idea of the existing additive manufacturing of metal materials is to pave the materials by two modes of spreading metal powder layer by layer or synchronously feeding powder in situ, melt the metal powder by a laser heat source, and finally solidify the metal powder into a metal part. Particularly, along with the introduction of various high-energy new energy carriers such as laser, electron beam and plasma, the time consumption of metal additive manufacturing is shorter and shorter, the metal additive manufacturing is more and more flexible in forming, and the metal additive manufacturing has the advantages of near-net-shape forming and complex part preparation, so that the additive manufacturing has great advantages in industries such as the aviation industry and the like with high requirements on part precision and high material melting point. But the deformation and cracking in formed parts due to various reasons has always been a stumbling block that limits metal 3D printing for large scale applications.

After the traditional metal material is subjected to hot working, internal stress is eliminated in a heat treatment mode, and the material performance is improved. Since the additive manufacturing is performed by laser/electron beam dot-by-dot printing and layer-by-layer advancing, the component not only bears local internal stress during the manufacturing process, but also is cumulatively superposed with structural stress, especially for refractory metal materials, stress concentration is easily formed, and thus the component is frequently cracked after or during the printing process. Thus, heat treating an additively manufactured component by conventional means clearly does not meet the requirements of timely on-line processing. To address this problem, the field of additive manufacturing technology has emerged as a Selective Laser Sintering (SLS) technique. The technology adopts a liquid-solid phase sintering mechanism as a metallurgical mechanism, partial melting of powder materials occurs in the forming process, solid phase cores of powder particles are reserved, and the compact forming process is realized through subsequent solid phase particle rearrangement and liquid phase solidification bonding. Although the strategy of incomplete melting of the powder can reduce the thermal stress accumulated by the forming material to a certain extent, the formed piece contains non-melted solid phase particles, and the process defects of high porosity, low density, poor tensile strength, high surface roughness and the like are directly caused.

Considering the development of laser technology, the selective laser melting technology currently selects a fiber laser with excellent beam mode, the laser power is 50-400W, and the power density reaches 5 multiplied by 10 ⁶ W/cm ² The powder laying technology is correspondingly improved. At present, in order to obtain a fully-compact laser piece, the laser piece is widely used for 3D printing of metal components and a selective melting mechanism for completely melting powder. On the basis of the mechanism, the patent application CN202010657447.1 designs a new selective laser melting device, and the scanning vector of laser is adjusted at any time through a temperature detector, so that the distribution of part energy is optimized, and the concentrated stress deformation is reduced; the laser focusing position is adjusted at any time by using an infrared distance meter, so that the laser focusing is accurate, and the melting effect is ensured; the protective gas flow velocity adjusting device is arranged, and the defects of metal parts caused by oxidation and spray are avoided. Although the technology has made a certain progress, the size and the temperature of the molten pool obviously have a certain difference under the same laser power because the particle size distribution of the current additive manufacturing powder is wide. Therefore, the laser energy distribution is regulated and controlled through temperature online test and feedback, and the requirement is high in the operation process. The application effect is therefore to be observed further.

It is clear from the foregoing that the deformation and cracking defects of 3D metal printing are caused by complex stresses such as thermal stress and structural stress due to repeated melting-rapid cooling of the micro molten pool during layer-by-layer printing. Once the defect is formed, it cannot be subsequently twisted. Therefore, it is the most desirable solution to reduce the cooling rate and perform simultaneous thermal treatment to eliminate thermal stress during 3D printing, which is the fundamental condition and precondition for avoiding and eliminating defect formation.

To remove thermal stress by an instantaneous and simultaneous heat treatment, several conditions must be met:

1. the temperature rise is rapid. The cooling speed of the micro molten pool generated by laser melting is high, and the micro molten pool is heated to the corresponding heat treatment temperature after being cooled and solidified, so that the existing or future defects are not compensated.

2. The heat area concentration is high. The size of the heated area is the size of a plurality of laser spot molten pools (the size of one laser spot is dozens of micrometers to one millimeter), because the boundary of the molten pool is frequently melted periodically and repeatedly in the process of melting the adjacent molten pools, the position where the thermal stress is most concentrated is mainly the boundary of the molten pool, and therefore, a heat source for heat treatment covers the boundaries of the molten pools as far as possible to achieve the effect of uniformly removing the thermal stress.

3. The limiting temperature can reach the heat treatment temperature. In order to be able to adapt to the heat treatment of most metals, in particular metals with a melting point above 2000 c, the limit temperature of the heat treatment is above 1000 c.

Rapid Thermal Processing (RTP) is a thermal processing mode with fast temperature rise and short heat preservation time. The infrared halogen lamp heating mode is small in size, light in weight, simple in structure and well matched with the laser printing head; the heating rate is high and can reach 100-150 ℃/S; the limit temperature is high, and the maximum temperature is more than or equal to 1200 ℃; the heat concentration is high, the radiation heating is realized, and the micro-area heating device is suitable for heating the molten pool surface of a micro-area. In addition, due to the online heat treatment mode of the infrared halogen lamp, the laser cladding process is not interfered by utilizing light heat transfer, and meanwhile, no additional gas substance is generated, and the laser printing atmosphere condition and impurity pollution are not damaged. Therefore, the infrared halogen lamp heating can effectively eliminate the thermal stress concentration caused by quenching. The method has great significance for eliminating the defects of welding seams and 3D printing components.

Disclosure of Invention

The invention aims to provide a 3D printing device and a method for eliminating printing defects by utilizing micro-area synchronous heat treatment, which can eliminate printing internal stress in time, eliminate fundamental conditions generated by cracks and ensure the additive manufacturing quality.

In order to realize the purpose, the invention adopts the following scheme:

the 3D printing device for eliminating the printing defects by utilizing the micro-area synchronous heat treatment comprises a 3D printing device body and an infrared halogen lamp; the infrared halogen lamp is arranged near a laser printing head of the 3D printing device body, the infrared halogen lamp is used for rapidly supplementing the temperature of the molten pool micro-area position which is melted by laser in the early stage in the laser processing process, so that the temperature of the molten pool micro-area is slowly reduced to a heat treatment temperature area, and the molten pool micro-area is gradually cooled to the room temperature after short-time heat treatment.

Further, the 3D printing device body comprises a powder feeder, a fiber laser, a laser gun body, a vacuum/inert atmosphere box body and a three-axis movable workbench; the laser gun body and the three-axis movable workbench are arranged in the vacuum/inert atmosphere box body, the three-axis movable workbench is positioned below the laser gun body and used for bearing a 3D printing product, the powder feeder and the optical fiber laser are arranged outside the vacuum/inert atmosphere box body and respectively connected with the laser gun body, and the infrared halogen lamp is arranged on one side of the laser gun body.

Furthermore, the infrared halogen lamp is installed on one side of the laser gun body through the position adjusting device, a coaxial powder feeding nozzle is arranged beside the laser gun body, the powder feeder is communicated with the coaxial powder feeding nozzle, and the infrared halogen lamp is arranged close to the coaxial powder feeding nozzle.

Further, the position adjusting device comprises a vertical moving shaft connected to the laser gun body, a horizontal moving shaft is connected to the vertical moving shaft in a sliding manner, and the infrared halogen lamp is installed below the horizontal moving shaft.

Further, the infrared halogen lamp is connected below the horizontal moving shaft through a connecting rod and a ball joint rotating shaft.

Further, the infrared halogen lamp is provided with a focus knob for adjusting the focus.

A3D printing method for eliminating printing defects by utilizing micro-area synchronous heat treatment is characterized in that an infrared halogen lamp is utilized to supplement temperature to a micro-area position of a molten pool melted in the early stage of laser in a laser processing process so as to slowly cool the micro-area position to a heat treatment temperature, and the solidification process of the molten pool is changed from the molten pool-solidification-room temperature quenching into the molten pool-solidification-in-situ heat treatment-cooling. Thermal stress is reduced by reducing the quenching speed of the molten pool, and 3D printing component defects are eliminated.

Further, the transient heat preservation temperature is 400-1200 ℃.

Further, the method comprises the following specific steps:

1) Vacuumizing or inflating the vacuum/inert atmosphere box body for protection;

2) Uniformly laying powder on a three-axis movable workbench through a powder feeder;

3) The laser moves along with the laser printing head to melt powder below the laser and form a micro molten pool; with the continuous movement of the laser, the former molten pool is cooled and solidified at the ambient temperature, and the powder melting and solidification process is completed;

4) The infrared halogen lamp quickly supplements heat to the micro-area position of the molten pool melted in the early stage of the laser and slowly cools the molten pool to the heat treatment temperature, and the molten pool is gradually cooled under the influence of external heat after the short heat treatment;

5) And repeating the steps 1) to 4) layer by layer until the construction printing is finished.

Laser welding and laser 3D printing technique have the characteristics that the zone by zone micro-district is printed, and the melting is removed point by point, and infrared halogen lamp heating has that the intensification is fast, the heat concentration is high and small, light in weight, simple structure, advantages such as the assembly is easy can realize printing with laser and realize good combination and complementation. The online timely heat supplement of the 3D printing molten pool in cooling is realized, the quenching degree is effectively reduced, the fundamental condition of crack generation is eliminated, and the component quality is improved.

The online post-heat-compensating laser printing head is used as an online post-heat-compensating source of the laser printing head, is arranged behind the laser printing head, synchronously moves forwards along with the laser printing head, and supplements heat in time by virtue of the characteristics of high speed, high energy accumulation and radiation heating, so that the quenching degree of a laser printing molten pool is reduced, the concentration of thermal stress is delayed, and meanwhile, online instantaneous heat treatment is realized. The mechanical property of the laser 3D printing component is improved. In view of the above-mentioned functions and assembly relationships of infrared halogen synchronous micro-zone heat treatment. The technical process flow is closely related to the laser 3D printing process. The basic technological process of laser 3D printing is vacuum/inflation protection, layer-by-layer powder spreading/synchronous powder feeding, laser layer-by-layer melting and point-by-point cooling.

According to the characteristics of 'point-by-point printing, layer-by-layer advancing and defect point-by-point accumulation' process of additive manufacturing, the invention realizes the micro-area synchronous heat treatment to eliminate the laser printing defect by virtue of the characteristics of rapid heating and temperature rise, high energy concentration, surface heating and laser adaptation of the infrared halogen lamp, and has the following advantages:

1. micro-zone simultaneous heat treatment

Aiming at the characteristics of 'point melting and rapid cooling solidification forming' of laser 3D printing, the micro-area synchronous heat treatment is adopted, so that online and timely transient heat treatment is realized, the rapid cooling speed of a point-shaped molten pool is obviously reduced, and the quality defect caused by heat stress accumulation is prevented;

2. non-contact, non-interference and non-pollution heat treatment

Aiming at the requirements of laser 3D printing environment, a light source radiation heating mode is adopted, so that the influence and the interference on the laser printing process are avoided, and the processing advantages and the component quality of the laser processing process, such as no contact, no interference and no pollution, are ensured;

3. dot heat treatment

The characteristic of high energy concentration of the infrared halogen lamp is utilized to realize the micro-area in-situ heat treatment in the solidification process of the laser micro-area molten pool, and the energy-saving effect is good.

The invention also has the following advantages:

1. good on-line adaptability

The laser and the infrared light source are used as heat sources, and the commonality of high concentration and quick heating and the energy matching are realized, so that high-energy laser point type melting and low-energy infrared point type heat treatment are realized, no interference exists between the laser and the infrared light source, the structure is simple, and the adaptability is good;

2. high efficiency

By using point type melting-solidification and point type online infrared light source heat treatment, the quenching degree of a laser melting pool is reduced, the thermal stress is reduced, the efficiency is high, and the instantaneity is good;

3. good effect

The additive manufacturing is combined with the point type on-line synchronous heat treatment as a point type accumulation manufacturing method, so that the adaptability is good, the timeliness is high, the internal stress is eliminated in time, the internal stress accumulation is avoided, and the additive manufacturing quality is ensured;

4. energy saving

Special or large equipment is not needed for carrying out reheating treatment after 3D printing; meanwhile, the integral heating is not needed, the overall heating power is low, and the energy-saving performance is good.

Drawings

FIG. 1 is an assembly view of an infrared halogen lamp heating and laser printhead

FIG. 2 is a schematic view of a laser gun body

In the figure: 1. the laser powder feeding device comprises a powder feeder, 2 parts of a fiber laser, 3 parts of a laser gun body, 4 parts of a vacuum/inert atmosphere box body, 5.3D printed products, 6 parts of a three-axis movable workbench, 31 parts of a lens, 32 parts of a vertical movable shaft, 33 parts of a horizontal movable shaft, 34 parts of a ball joint rotating shaft, 35 parts of a focal length knob, 36 parts of an infrared halogen lamp and 37 parts of a coaxial powder feeding nozzle.

Detailed Description

The present invention will now be described in further detail with reference to specific examples, which are intended to be illustrative, but not limiting, of the invention.

As shown in fig. 1, the 3D printing apparatus for eliminating printing defects by using micro-zone simultaneous thermal processing according to the present invention includes a powder feeder 1, a fiber laser 2, a laser gun body 3, a vacuum/inert atmosphere box 4, a three-axis moving table 6, a lens 31, a vertical moving axis 32, a horizontal moving axis 33, a ball joint rotating axis 34, a focus knob 35, an infrared halogen lamp 36, and a coaxial powder feeding nozzle 37.

The laser gun body 3 and the three-axis movable workbench 6 are arranged in the vacuum/inert atmosphere box body 4, the three-axis movable workbench 6 is positioned below the laser gun body 3 and is used for bearing a 3D printing product 5, the powder feeder 1 and the optical fiber laser 2 are arranged outside the vacuum/inert atmosphere box body 4 and are respectively connected with the laser gun body 3; the powder feeder 1, the optical fiber laser 2, the laser gun body 3, the vacuum/inert atmosphere box body 4 and the three-axis movable worktable 6 jointly form a 3D printing device body.

As shown in fig. 2, an infrared halogen lamp 36 is installed on one side of the laser gun body 3 through a position adjusting device, the infrared halogen lamp 36 is arranged close to a coaxial powder feeding nozzle 37, laser generated by the fiber laser 2 is focused on the 3D printed product 5 on the three-axis moving table 6 through a lens 31, and the infrared halogen lamp 36 is used for performing heat treatment during solidification of a laser micro-area molten pool in the laser processing process.

As shown in fig. 2, the position adjusting device includes a vertical moving shaft 32 connected to the laser gun body 3, a horizontal moving shaft 33 slidably connected to the vertical moving shaft 32, an infrared halogen lamp 36 connected below the horizontal moving shaft 33 through a link and a ball joint rotating shaft 34, position adjustment of the infrared halogen lamp 36 in the vertical direction and the horizontal direction is realized through the vertical moving shaft 32 and the horizontal moving shaft 33, and adjustment of the projection angle of the infrared halogen lamp 36 is realized through the ball joint rotating shaft 34. The infrared halogen lamp 36 is provided with a focus knob 35 for adjusting a focus, and a focusing effect can be adjusted by the focus knob 35.

The 3D printing method for eliminating the printing defects by utilizing the synchronous heat treatment of the micro-areas comprises the following steps:

vacuum/inflation-powder laying/synchronous powder feeding-laser melting layer by layer-infrared halogen lamp on-line micro-area heat treatment-point by point cooling. The specific process is described as follows:

1. vacuum/gas filling

The general laser printing process needs to be carried out in a closed environment, and in order to prevent the influence of the atmosphere in the laser printing process, a vacuum/inert atmosphere box body is subjected to vacuum pumping or inflation protection. Aeration is generally dominated by inert gases;

2. powder spreading/synchronous powder feeding

Spheroidized powder is uniformly spread on a three-axis moving worktable in the same height through a powder feeder 1.

3. Laser melting

The laser moves with the laser printhead, melting the powder under the laser and forming a micro-puddle. With the continuous movement of the laser, the former molten pool is cooled and solidified at the ambient temperature, and the powder melting and solidification process is completed.

4. On-line micro-area heat treatment of infrared halogen lamp

The infrared halogen lamp is installed behind the laser print head and moves synchronously with the movement of the laser print head. By means of the characteristics of fast temperature rise and high heat energy concentration, the infrared halogen lamp can quickly supplement heat to raise the molten pool micro-area position melted in the early stage of laser to the heat treatment temperature, and the highest temperature can reach 1200 ℃. Since the infrared halogen lamp heating range is much larger than the laser melt pool range. Thereby allowing the bath to cool gradually under the influence of external heat.

5. Repeating the above steps layer by layer

And repeating the process by combining the laser and the infrared halogen lamp heat treatment until the construction and the printing are finished.

In the process. Because of the combination of laser and on-line heat treatment of infrared halogen lamp, the solidification process of molten pool is converted from melting point-room temperature quenching of traditional laser printing into melting pool-cooling-in-situ heat treatment-solidification. The quenching degree of a molten pool is effectively reduced, the concentration of thermal stress is reduced, and the defect of a 3D printing component formed by overhigh internal stress is eliminated.

Claims (9)

1. Utilize the synchronous thermal treatment in subregion to eliminate 3D printing device who prints the defect, its characterized in that: the three-dimensional printing device comprises a 3D printing device body and an infrared halogen lamp (36); the infrared halogen lamp (36) is arranged near a laser printing head of the 3D printing device body, and the infrared halogen lamp (36) is used for heating the molten pool micro-area position which is melted by the laser in the early stage to the heat treatment temperature in the laser processing process so as to cool the molten pool step by step and reduce the supercooling degree of the molten pool.

2. The 3D printing apparatus for eliminating printing defects by using micro-zone synchronous thermal processing according to claim 1, wherein: the 3D printing device body comprises a powder feeder (1), a fiber laser (2), a laser gun body (3), a vacuum/inert atmosphere box body (4) and a three-axis movable workbench (6); the laser gun body (3) and the three-axis movable workbench (6) are arranged in the vacuum/inert atmosphere box body (4), the three-axis movable workbench (6) is located below the laser gun body (3) and used for bearing a 3D printed product (5), the powder feeder (1) and the optical fiber laser (2) are arranged outside the vacuum/inert atmosphere box body (4) and respectively connected with the laser gun body (3), and the infrared halogen lamp (36) is installed on one side of the laser gun body (3).

3. The 3D printing apparatus for eliminating printing defects using micro-zone synchronous thermal processing according to claim 2, wherein: the infrared halogen lamp (36) is installed on one side of the laser gun body (3) through the position adjusting device, a coaxial powder feeding nozzle (37) is arranged beside the laser gun body (3), the powder feeder (1) is communicated with the coaxial powder feeding nozzle (37), and the infrared halogen lamp (36) is arranged close to the coaxial powder feeding nozzle (37).

4. The 3D printing device for eliminating printing defects by utilizing micro-zone synchronous thermal treatment according to claim 3, wherein: the position adjusting device comprises a vertical moving shaft (32) connected to the laser gun body (3), a horizontal moving shaft (33) is connected to the vertical moving shaft (32) in a sliding mode, and an infrared halogen lamp (36) is installed below the horizontal moving shaft (33).

5. The 3D printing apparatus for eliminating printing defects by using micro-zone synchronous thermal processing according to claim 4, wherein: the infrared halogen lamp (36) is connected below the horizontal moving shaft (33) through a connecting rod and a ball joint rotating shaft (34).

6. 3D printing device for eliminating printing defects by means of micro-zone synchronized thermal processing according to any of claims 1 to 5, characterized in that: the infrared halogen lamp (36) is provided with a focal length knob (35) for adjusting the focal length.

7. A 3D printing method for eliminating printing defects by using micro-zone synchronous thermal processing based on the 3D printing apparatus of claim 1, wherein: in the laser processing process, an infrared halogen lamp (36) is used for supplementing the temperature of the micro-area position of the molten pool melted in the early stage of the laser to the heat treatment temperature, so that the solidification process of the molten pool is changed from the molten pool-solidification-room temperature quenching into the molten pool-cooling-in-situ heat treatment-solidification. The 3D printing component cracking defect is eliminated by reducing the quenching degree of the molten pool to reduce the thermal stress.

8. The 3D printing method for eliminating printing defects using micro-zone synchronous thermal processing according to claim 7, wherein: the transient heat preservation temperature is 400-1200 ℃.

9. The 3D printing method for eliminating printing defects by utilizing micro-zone synchronous thermal treatment according to claim 7, characterized by comprising the following specific steps:

1) Vacuumizing or inflating the vacuum/inert atmosphere box body for protection;

2) Uniformly spreading the powder on a three-axis movable workbench through a powder feeder;

3) The laser moves along with the laser printing head to melt powder below the laser and form a micro molten pool; with the continuous movement of the laser, the former molten pool is cooled, quenched and solidified at the ambient temperature to complete the powder melting and solidification process;

4) The infrared halogen lamp quickly supplements heat to heat the micro-area position of the molten pool melted in the early stage of the laser to the heat treatment temperature, so as to realize the step-by-step cooling and reduce the quenching degree and the quenching effect;

5) And repeating the steps 1) to 4) layer by layer until the construction printing is finished.

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