CN107685149B - A kind of method and device improving laser gain material manufacture thin-wall part forming quality - Google Patents

Abstract

The invention provides a method and a device for improving the forming quality of a thin-walled part in laser additive manufacturing. The device includes a mobile platform system, a laser metal deposition system, an auxiliary forming system, an active cooling system and a central control system. The forming method is that when the laser metal deposition system is cladding and forming thin-walled parts, the auxiliary forming system controls the thickness and forming direction of the thin-walled parts in real time. Due to the problem that the surface roughness of the interlayer accumulation is too large, the wall forming realizes the processing of straight and curved thin walls with variable thickness. At the same time, the active cooling system cools down the deposition layer in real time. The invention solves the problems of low surface quality of laser cladding forming, thermal stress accumulation and cracking of the deposited layer due to temperature increase during continuous multi-layer deposition, low forming efficiency caused by coarse microstructure and slow cooling, etc. Quality, efficient forming.

Description

A method and device for improving the forming quality of thin-walled parts in laser additive manufacturing

technical field

The invention belongs to the technical field of laser additive manufacturing, and in particular relates to a method and a device for improving the forming quality of thin-walled parts in laser additive manufacturing.

Background technique

At present, metal additive manufacturing technology mainly includes electron beam wire melting technology, electron beam selective melting technology, laser selective melting technology and laser cladding forming technology. Electron beam wire melting technology and electron beam selective melting technology require high environmental vacuum and small forming space, thus limiting the size of the formed parts, and for complex and thin-walled parts, due to the thicker arc column, the forming accuracy Poor, the fineness, precision and thin wall of the forming are not as good as the laser cladding method, and it is difficult to obtain finer and thinner parts than the laser cladding forming. The laser selective melting technology is cladding by powder spreading, the powder utilization rate is not high, and the size requirements of the formed parts cannot be too large. The laser cladding forming technology adopts the powder feeding method for cladding forming, the powder utilization rate is high, and the forming space is not limited, and it can be applied to the cladding forming of large-sized and complex parts. research hotspot. (See literature: Huang C, Lin X, Liu F, et al. Effects of cooling condition on microstructure and mechanicalproperties in laser rapid forming of 34CrNiMo6thin-wall component[J]. The International Journal of Advanced Manufacturing Technology, 2016, 82(5): 1269-1279). The large thin-walled blades used in aero-engines, steam turbines, and compressors are usually manufactured by traditional milling due to their complex curved surface shapes and high precision requirements. Literature: Gasser A, Backes G, Kelbassa I, et al. Laser Additive Manufacturing: Laser Metal Deposition (LMD) and Selective Laser Melting (SLM) in Turbo-Engine Applications [J]. Laser Technik Journal, 2010, 7(2):58 -63). The laser cladding forming technology is based on the three-dimensional digital model of the formed component, and the component is formed by layer-by-layer deposition of laser cladding metal powder, which greatly shortens the design and manufacturing cycle, does not require molds, and has high material utilization. It has broad application prospects in terms of parts (see literature: Qiu C, Ravi G A, Dance C, et al. Fabrication of large Ti–6Al–4V structures by direct laser deposition [J]. Journal of Alloys&Compounds, 2015, 629:351- 361).

Laser cladding has been applied to the manufacture of some important large parts, but there are still many problems in the manufacture of micro and thin-walled metal components. For example, since the size of the molten pool of the laser cladding deposition process is generally 2-3mm, even if the current relatively mature laser near-net-shape (LENS) process has a minimum molten pool of 1mm, the minimum feature size of the formed parts is 0.63 mm. mm, there is a limit to the accuracy of forming thin-walled parts (see literature: Yao Bo, Ma Xulong, Ge Wenjun, et al. Microstructure and performance analysis of TC4 thin-walled parts formed by laser micro-cladding deposition [C], National Conference on Special Processing. 2013 ). Secondly, there are concave-convex peaks caused by the overlap between layers in the laser deposition layer, resulting in low surface quality of the formed parts. Therefore, the thin-walled parts produced by the general laser cladding forming process need to be rewashed and polished before they can meet the requirements for use. In addition, the Chinese patent application number: 201610408053.6 titled "Arc-filling additive manufacturing method for inclined thin-walled structural parts" points out that when a single-track inclined thin-walled part is stacked, the molten pool may flow between the deposition layers due to excessive offset. problem, reducing the forming accuracy. The auxiliary forming system of this device can adjust the opening and closing size and angle of the two-piece ceramic block through a high-precision mechanical arm, so as to ensure that the laser deposition molten pool is always solidified and formed in the two-piece ceramic block, which can not only break through the limit size of the molten pool and form thin walls It can improve the surface quality of thin-walled parts, and can also overcome the problem of molten pool flow caused by interlayer accumulation by controlling the thickness and forming direction of thin-walled parts in real time.

When the thin-walled parts are formed by laser cladding, because the parts undergo periodic, violent, unsteady, and cyclic heating of the high-energy laser beam for a long time, the temperature of the deposition layer increases cumulatively, resulting in a high level of internal stress in the parts, evolution and interaction process The extremely complex coupling effect of thermal stress, phase transformation stress and confinement stress and their stress concentration can easily lead to warpage and cracking of thin-walled parts (see reference: Wang Huaming. Laser additive manufacturing of high-performance large-scale metal components: some basic material problems [ J]. Journal of Aeronautics and Astronautics, 2014, 35(10): 2690-2698), therefore, timely cooling of the deposition layer is necessary to improve the quality of the cladding layer. The active cooling system in this device performs real-time active cooling of the laser cladding deposition layer by positioning and spraying liquid nitrogen. The cooling rate and solidification rate of the molten pool can reduce the microstructure size of the cladding layer and refine the grains. Research shows (see literature: Farshidianfar M H, Khajepour A, Gerlich A P. Effect of Real-time Cooling Rate on Microstructure in Laser Additive Manufacturing [J]. Journal of Materials Processing Technology, 2016, 231: 468-478): Many mechanical properties depend on the size and shape of the grains and microstructure. Refinement of the grains is beneficial to the fracture sensitivity during laser cladding deposition and improves the elongation at break of the cladding (see: Brandl E, Schoberth A,Leyens C.Morphology,microstructure,and hardness of titanium(Ti-6Al-4V)blocks deposited by wire-feed additive layer manufacturing(ALM)[J].Materials Science&Engineering A,2012,532(3):295- 307). In addition, the deposition process does not require a slow cooling process, and the laser cladding deposition process can be uninterrupted, thereby improving the forming efficiency.

Through the literature search of the prior art, it was found that the Chinese Patent Application No.: 201610408053.6, titled "Arc Wire Filling Additive Manufacturing Method for Inclined Thin-Walled Structural Parts", provides an arc-filling wire-filling additive manufacturing method for inclined thin-walled structural parts. The method The stacking and forming of multi-layer single-channel inclined thin-walled structural parts is realized by adjusting the offset and the angle with the substrate in real time. However, this method is not suitable for the manufacture of large-angle inclined thin-walled parts, and has a certain limit on the lateral offset, and is also not suitable for the manufacture of variable-thickness inclined thin-walled parts. Chinese Patent Application No.: 20161030234, titled "Parts and Die Deposition Processing and Manufacturing Method", this method adopts arc or electron beam and laser beam composite process to form parts and molds with thin-walled or fine parts, however, this method The formed parts still need to be finished by milling, grinding or polishing to meet the dimensional accuracy requirements and surface accuracy requirements of the workpiece to be formed. Chinese Patent Application No.: 201510118939.2, titled "Method and Device for Controlling Microstructure Growth During Laser Cladding of Single Crystal Alloys", uses low-temperature airflow to actively cool the process of laser cladding repairing nickel-based single crystal turbine blades. The temperature gradient perpendicular to the blade tip enhances the epitaxial growth capability of the single crystal structure. However, this method is limited to the field of repairing single crystal blades, and the cooling rate of low-temperature airflow is limited. Therefore, it is of great significance to propose a method and device for improving the forming quality of thin-walled parts in laser additive manufacturing.

SUMMARY OF THE INVENTION

Aiming at the deficiencies in the prior art, the present invention provides a device and method for improving the forming quality of thin-walled parts manufactured by laser additive materials, which solves the problem that the limit size of the molten pool existing in the existing laser additive manufacturing thin-walled parts has an impact on forming thin-walled parts. In order to manufacture thin-walled components with high efficiency and high quality, the accuracy limitations of the size of the parts, poor surface quality of cladding forming, low efficiency, thermal stress accumulation and cracking of continuous multilayer cladding deposits, and coarse microstructures can be avoided.

In order to achieve the above object, the technical scheme provided by the invention is:

A device for improving the forming quality of thin-walled parts in laser additive manufacturing, comprising a mobile platform system, a laser metal deposition system, an auxiliary forming system, an active cooling system and a central control system,

The mobile platform system includes a fixed worktable, a three-axis mobile platform and a high-precision mechanical arm, the three-axis mobile platform and the high-precision mechanical arm are mounted on the fixed worktable, and a workpiece fixture is mounted on the three-axis mobile platform;

The laser metal deposition system includes a laser, a laser head, a powder feeder and a powder nozzle, the powder nozzle is connected to the powder feeder through a powder feeding copper tube, and the powder nozzle and the laser head are mounted on a high-precision mechanical arm;

The auxiliary forming system includes two pieces of ceramic blocks, the two pieces of ceramic blocks are fixed on the mechanical gripper through the gripper clamp, and the two pieces of ceramic blocks are arranged oppositely, and the mechanical gripper is mounted on the high-precision mechanical arm;

The active cooling system includes a liquid nitrogen spray nozzle, an electromagnetic control valve, and a liquid nitrogen tank. The liquid nitrogen spray nozzle is installed behind the laser head and connected to the liquid nitrogen tank. The liquid nitrogen spray nozzle and the liquid nitrogen tank are arranged between the liquid nitrogen spray nozzle and the liquid nitrogen tank. With electromagnetic control valve;

The three-axis mobile platform, high-precision robotic arm, powder feeder, laser and electromagnetic control valve are all connected to the central control system; the central control system can realize the opening and closing of ceramic blocks by controlling the linkage between the high-precision robotic arm and the mechanical gripper. For angle adjustment, the injection of liquid nitrogen is controlled by adjusting the opening and closing of the solenoid valve, and the laser cladding deposition layer is actively cooled rapidly. At the same time, the powder feeding amount, laser power and scanning speed are adjusted in real time.

Further, the two ceramic blocks are respectively fixed on the gripper clamp by fastening bolts, and the gripper clamp is mounted on the mechanical gripper.

Further, the ceramic block is made of nano-alumina material and can work stably at a high temperature of 1600°C.

Further, the laser is a fiber laser.

The device for improving the forming quality of laser additive manufacturing thin-walled parts realizes the method for laser cladding deposition of thin-walled parts, which is characterized by comprising the following steps:

Step 1: Build the component CAD geometric model according to the expected three-dimensional shape and size of the thin-walled part, extract the STL model of the thin-walled part, and then select the layer thickness according to the shape and size of the component, and use the layered slice software to layer the STL model. deal with;

Step 2: Determine the laser power, powder feeding amount, scanning speed and deposition height h _n of the laser deposition layer of this layer according to the layering of step 1, and adjust the distance between the two ceramic blocks and the thin-walled parts through a high-precision robotic arm. The width is the same, and the rotation angle of the two ceramic blocks is adjusted in real time according to the bending shape of the thin-walled part, so as to ensure that the laser deposition molten pool is always solidified between the two ceramic blocks;

Step 3: According to the requirements of the deposition height h _n in step 2 and the expected lower deposition layer height and bending angle of the thin-walled part, re-adjust the laser power, powder feeding amount, scanning speed, deposition height h _n+1 and The distance between the two ceramic blocks, the rotation angle, the lower layer cladding forming, and the layer by layer laser cladding deposition, until the entire thin-walled part is formed to meet the requirements; in the process of each layer of laser cladding deposition, the central control system By controlling the opening and closing of the solenoid valve, the injection amount of liquid nitrogen is controlled, and each layer of the laser cladding deposition layer is actively cooled in real time, so as to avoid the problems of thermal stress accumulation and cracking of the deposition layer and coarse microstructure caused by the temperature increase in the next deposition. .

Further, the deposition of the lower layer does not require a slow cooling process, and the laser cladding deposition process can be repeated without interruption.

Further, the thin-walled part is a straight-faced thin-walled part, a variable-thickness thin-walled part or a curved thin-walled part.

Beneficial effects of the present invention:

①The auxiliary forming system of this device can adjust the opening and closing size and angle of the two-piece ceramic block through the linkage of the high-precision mechanical arm and the mechanical gripper, so as to ensure that the laser deposition molten pool is always solidified and formed in the two-piece ceramic block. The limit size of the pool limits the accuracy of the formed thin-walled parts, improves the surface quality of the thin-walled parts, and can overcome the problem of molten pool flow caused by interlayer accumulation by controlling the thickness and forming direction of the thin-walled in real time.

② The active cooling system in this device performs real-time active cooling of the laser cladding deposition layer by spraying liquid nitrogen, which can not only effectively solve the problems of thermal stress accumulation and cracking caused by the cumulative increase in the temperature of the deposition layer, but also can greatly improve the cooling effect of liquid nitrogen. Increase the cooling rate and solidification rate of the molten pool, thereby reducing the microstructure size of the cladding layer and refining the grains. In addition, the deposition process does not require a slow cooling process, and can achieve uninterrupted laser cladding forming, thereby improving the forming efficiency.

③ The present invention makes full use of the characteristics of laser cladding forming for additive manufacturing, combined with the auxiliary forming system and active cooling system in the device, to achieve high-quality and efficient forming of variable thickness straight surfaces and curved thin walls, and save expensive powder. materials, the advantages of shortening the development and manufacturing cycle of complex thin-walled parts.

Description of drawings

FIG. 1 is a schematic structural diagram of the device for improving the forming quality of thin-walled parts in laser additive manufacturing according to the present invention.

FIG. 2 is a schematic state diagram of a double-piece open-close ceramic block device when laser cladding is used to manufacture thin-walled parts with different structures.

FIG. 3 is a schematic view of the structure of the gripper clamp.

In the picture:

1. Fixed table; 2. Three-axis mobile platform; 3. Workpiece fixture; 4. High-precision robotic arm; 5. Auxiliary forming system; 6. Liquid nitrogen nozzle; 7. Electromagnetic control valve; 8. Liquid nitrogen tank; 9 . Powder nozzle; 10. Powder feeder; 11. Laser head; 12. Laser; 13. Central control system; 15. Gripper clamp; 15-2. Fastening bolt; 15-1. Clamp block; 16. Straight face Wall parts; 17. Variable thickness thin-walled parts; 18. Curved thin-walled parts.

Detailed ways

The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited thereto.

As shown in FIG. 1 , a device for improving the forming quality of thin-walled parts in laser additive manufacturing of the present invention includes a mobile platform system, a laser metal deposition system, an auxiliary forming system, an active cooling system and a central control system.

The mobile platform system includes a fixed worktable 1, a three-axis mobile platform 2, a high-precision mechanical arm 4 and a mechanical gripper. On the fixed worktable 1, the three-axis moving platform 2 is installed with a workpiece fixture 3, and the workpiece fixture 3 clamps and fixes the substrate by means of fastening bolts. The laser metal deposition system includes a fiber laser 12, a laser head 11, a powder feeder 10 and a powder nozzle 9. The powder nozzle 9 is connected to the powder feeder 10 through a powder feeding copper tube. The powder nozzle 9 and the laser head 11 are installed on high-precision machinery. On the arm 4, the three-axis mobile platform 2 and the high-precision mechanical arm 4 are linked and cooperated to realize the laser cladding deposition forming at different points and different angles in the three-dimensional space. At the same time, the parameters of the fiber laser 12 and the powder feeding amount of the powder feeder 10 can be adjusted in real time according to the specific characteristics of the parts, so as to realize laser cladding forming deposition with different wall thicknesses.

The auxiliary forming system 5 includes two ceramic blocks, which are made of nano-alumina material and can work stably at a high temperature of 1600°C. Two ceramic blocks are mounted on the mechanical gripper through gripper clamps 15 . The gripper clamp 15 includes fastening bolts 15-2 and a clamp block 15-1, and two ceramic blocks are respectively fixed on the clamp block 15-1 by the fastening bolts 15-2. The robotic gripper is mounted on the high-precision robotic arm 4 . Through the linkage between the high-precision robotic arm 4 and the mechanical gripper, the opening and closing size of the two ceramic blocks can be adjusted to be consistent with the width of the thin-walled part, and the rotation angle of the ceramic block can be adjusted in real time according to the curved shape of the thin-walled part to ensure that the laser deposition molten pool is always in The two ceramic blocks are solidified inside to complete the auxiliary forming of the laser cladding deposition process. FIG. 2 shows the state of two ceramic blocks when three different thin-walled parts 16 , variable-thickness thin-walled parts 17 , and curved thin-walled parts 18 are formed by laser cladding of the device according to the present invention.

The active cooling system includes a liquid nitrogen nozzle 6, an electromagnetic control valve 7, and a liquid nitrogen tank 8. The liquid nitrogen nozzle 6 is installed behind the laser head 11, and the injection amount of liquid nitrogen is controlled by the opening and closing of the electromagnetic valve to actively deposit metal. The layer cools quickly.

The three-axis mobile platform 2, the high-precision mechanical arm 4, the mechanical gripper, the powder feeder 10, the laser 12 and the electromagnetic control valve 7 are all connected to the central control system 13, so that the central control system 13 can control the mobile platform system through a programmable program , Laser metal deposition system, auxiliary forming system, active cooling system functions, to achieve coordinated work between each system, flexible operation.

Specifically, the specific process of the above-mentioned device for laser cladding and forming of thin-walled parts is as follows:

According to the three-dimensional shape and size of the complex thin-walled parts, the CAD geometric model of the component is established, the STL model of the thin-walled part is extracted, and then the layer thickness is selected according to the shape and size of the component, and the STL model is layered by using layered slicing software. The programmable program is input into the central control system 13 to generate a scan path. The substrate is fixed on the three-axis moving platform 2 through the workpiece fixture 3 . According to the height h _n and width of the deposition layer of the chemical layer, the central control system 13 controls the laser power and powder feeding amount of the laser deposition layer in real time by controlling the fiber laser 12 and the powder feeder 10. In addition, by controlling the three-axis moving platform 2, The high-precision robotic arm 4 and the robotic gripper are linked together to achieve laser cladding deposition at different points and angles in three-dimensional space. At the same time, according to different characteristic parts of complex thin-walled parts, such as straight-faced thin-walled parts 16 , variable-section thin-walled parts 15 , and curved thin-walled parts 15 . The central control system 13 controls the high-precision mechanical arm 4 and the mechanical gripper to cooperate with each other to adjust the distance between the two ceramic blocks to be consistent with the width of the thin-walled part, and to adjust the rotation angle of the two ceramic blocks in real time according to the curved shape of the thin-walled part. Ensure that the laser cladding deposition molten pool is always solidified in the two-piece ceramic block device, as shown in Figure 2.

According to the requirements of the deposition height h _n in step 2 and the expected lower deposition layer height and bending angle of the thin-walled part, the laser power, powder feeding amount, scanning speed, deposition height h _n+1 and two The distance between the ceramic blocks and the rotation angle, the lower layer cladding is formed, and the laser cladding is deposited layer by layer until the entire thin-walled part is formed to meet the requirements; in the process of each layer of laser cladding, the central control system 13 passes through The opening and closing of the solenoid valve is controlled to control the injection amount of liquid nitrogen, and each layer of the laser cladding deposition layer is actively cooled in real time to avoid the problems of thermal stress accumulation and cracking of the deposition layer and coarse microstructure caused by the temperature increase in the next deposition. The lower layer deposition does not require a slow cooling process, and the laser cladding deposition process can be repeated without interruption.

The embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above-mentioned embodiments, and any obvious improvement, replacement or Modifications all belong to the protection scope of the present invention.

Claims (4)

1. A device for improving the forming quality of laser additive manufacturing thin-walled parts to realize a method for laser cladding deposition of thin-walled parts, characterized in that the device for improving the forming quality of thin-walled parts by laser additive manufacturing comprises a mobile platform system , laser metal deposition system, auxiliary forming system (5), active cooling system and central control system (13), The mobile platform system includes a fixed workbench (1), a three-axis mobile platform (2) and a high-precision mechanical arm (4), and the three-axis mobile platform (2) and the high-precision mechanical arm (4) are mounted on the fixed workbench ( 1), a workpiece fixture (3) is installed on the three-axis mobile platform (2); The laser metal deposition system comprises a laser (12), a laser head (11), a powder feeder (10) and a powder nozzle (9), and the powder nozzle (9) is connected to the powder feeder (10) through a powder feeding copper pipe, Both the powder nozzle (9) and the laser head (11) are mounted on the high-precision robotic arm (4); The auxiliary forming system (5) includes two ceramic blocks, the ceramic blocks are made of nano-alumina material, the two ceramic blocks are fixed on the mechanical gripper by the gripper clamp (15), and the two ceramic blocks are opposite to each other. set, the mechanical gripper is mounted on the high-precision mechanical arm (4); The active cooling system includes a liquid nitrogen spray nozzle (6), an electromagnetic control valve (7), and a liquid nitrogen tank (8). The liquid nitrogen spray nozzle (6) is installed behind the laser head (11) and is connected to the liquid nitrogen tank. (8) connection, an electromagnetic control valve (7) is arranged between the liquid nitrogen spray nozzle (6) and the liquid nitrogen tank (8); The three-axis moving platform (2), the high-precision robotic arm (4), the powder feeder (10), the laser and the electromagnetic control valve (7) are all connected to the central control system (13); the central control system (13) controls the high The linkage and cooperation of the precision mechanical arm (4) and the mechanical gripper can realize the adjustment of the opening and closing size and angle of the ceramic block. By adjusting the opening and closing of the electromagnetic control valve (7), the injection of liquid nitrogen is controlled, and the laser cladding deposition layer is actively and rapidly cooling, and at the same time adjust the powder feeding amount, laser power and scanning speed in real time; Include the following steps: Step 1: Build the component CAD geometric model according to the expected three-dimensional shape and size of the thin-walled part, extract the STL model of the thin-walled part, and then select the layer thickness according to the shape and size of the component, and use the layered slice software to layer the STL model. deal with; Step 2: Determine the laser power, powder feeding amount, scanning speed and deposition height h _n of the laser deposition layer of this layer according to the layering of step 1, and adjust the distance between the two ceramic blocks by the high-precision robotic arm (4). The width of the thin-walled parts is the same, and the rotation angle of the two ceramic blocks is adjusted in real time according to the curved shape of the thin-walled parts to ensure that the laser deposition molten pool is always solidified between the two ceramic blocks; Step 3: According to the requirements of the deposition height h _n in step 2 and the expected lower deposition layer height and bending angle of the thin-walled part, re-adjust the laser power, powder feeding amount, scanning speed, and deposition height h _n through the predetermined program of the central control system (13). ₊₁ and the distance and rotation angle between the two ceramic blocks, the lower layer cladding is formed, and the laser cladding is deposited layer by layer until the entire thin-walled part is formed to meet the requirements; in the process of each layer of laser cladding deposition, The central control system (13) controls the injection amount of liquid nitrogen by controlling the opening and closing of the electromagnetic valve, and actively cools each layer of the laser cladding deposition layer in real time, so as to avoid the thermal stress accumulation of the deposition layer caused by the temperature increase during the next deposition Cracking, coarse microstructure problems. 2 . The method for laser cladding deposition according to claim 1 , wherein the deposition of the lower layer does not require a slow cooling process, and the laser cladding deposition process can be repeated without interruption. 3 . 3 . The method for laser cladding deposition according to claim 1 , wherein the thin-walled part is a straight-faced thin-walled part. 4 . 4 . The method for laser cladding deposition according to claim 1 , wherein the thin-walled part is a variable-thickness thin-walled part or a curved thin-walled part. 5 .