WO2023142212A1 - Device and method for mitigating problem of workpiece edge subside by means of closed-loop control of laser power - Google Patents

Abstract

The present invention relates to the field of laser cladding quality monitoring, and in particular to a device and method for mitigating a problem of workpiece edge subside by means of closed-loop control of laser power. According to the present invention, in the laser cladding process, a coaxial infrared camera is used for detecting and acquiring a molten pool image in a vertical direction, and a molten pool width value is obtained after image processing. A difference between a measured real-time fusion width and a reference value fusion width serves as an input variable of a PID controller, and laser power is regulated and controlled by means of a combination of three control components comprising proportion, differential, and integration, and then is fed back to a laser directional energy deposition system. The method accelerates grain equiaxing by improving the thermal gradient, effectively inhibits increase of the molten pool width and accumulation of the thermal effect, can significantly mitigate the problem of workpiece edge subside, improves the cladding quality and material performance, and prolongs the service life.

Description

A device and method for closed-loop control of laser power to improve workpiece sagging technical field

The invention relates to the field of laser cladding quality monitoring, in particular to a device and method for closed-loop control of laser power to improve workpiece sagging. Using infrared camera real-time monitoring and PID algorithm closed-loop control method to adjust the laser power, improve the heat accumulation effect of the molten pool and the edge collapse of the workpiece, and improve the cladding quality and material performance.

Background technique

Laser Directed Energy Deposition technology is a new processing technology developed in the mid-1980s. It uses layer-by-layer surfacing to manufacture dense metal components. Because it can quickly and accurately manufacture structural parts with complex shapes, the manufacturing cost It has outstanding characteristics such as low cost and high forming efficiency, and shows obvious advantages in the rapid prototyping technology of large-scale and complex parts, and has broad application prospects in aerospace, automobile and ship fields.

The high-energy laser is irradiated on the substrate, melting the surface of the substrate and the powder forms a molten pool on the substrate. There are heat exchange and shape changes inside the molten pool. It is characterized by high temperature, high brightness, small size and fast change speed. The formation of the molten pool helps to determine the grain growth in the solidification microstructure and is one of the main factors determining the surface quality of the coating, so the monitoring of the molten pool state is very important. Among them, the width of the molten pool is an important factor reflecting the state of the molten pool. Affected by the cumulative heat effect of the molten pool, the workpiece often has edge sagging in the actual cladding process, which seriously affects the surface quality and mechanical properties of the workpiece.

Contents of the invention

In order to solve the above problems, the present invention proposes a method for closed-loop control of laser power to improve the problem of workpiece sag, which is characterized in that: during the laser cladding process, a coaxial infrared camera is used to detect and obtain the image of the molten pool in the vertical direction, and the image is The melt pool width value is obtained after processing. The difference between the detected real-time melting width and the reference value melting width is used as the input variable of the PID controller, and the laser power is jointly regulated through the three control components of proportionality, differential and integral, and then fed back to the laser directed energy deposition system; Gradients can be used to accelerate the equiaxation of grains, effectively inhibit the growth of molten pool width and the accumulation of thermal effects, and can significantly improve the problem of workpiece sag, improve cladding quality and material properties, and prolong service life.

Device of the present invention is made up of following parts:

(1) Laser directed energy deposition system: The laser directed energy deposition system consists of a laser source, a water-cooled protector, a numerical control platform, a powder feeder, a protective gas cylinder, a laser processing head, and a motion mechanism. The laser processing head is connected to the numerical control platform through the movement mechanism, and the parameters are set by the numerical control platform to make the laser processing head move in XYZ three-axis multi-direction. The laser processing head integrates the powder feeding channel, the air supply channel, the optical channel and the water cooling channel. The high-energy laser is generated in the laser source, then emitted from the light exit hole of the nozzle of the laser processing head, and then focused on the substrate plane. The powder feeder, protective gas cylinder, and water-cooled protector are all connected to the CNC platform through electricity.

(2) Melting width online monitoring system: The infrared camera body is equipped with Ethernet connector, IO interface, SD memory card cover, water cooling interface, LED warning light, focusing mechanism optical device and head connection. The infrared camera junction box with multi-IO port cables is electrically connected to the power supply, and the infrared camera is coaxially installed on the laser processing head through its head connection. Connect to the water-cooling protector through the water-cooling interface, and use an Ethernet switch to connect to the PC through the Ethernet connector.

(3) Data acquisition and image processing system: On the PC side, Labview is used to integrate the data acquisition and image processing system to realize online monitoring of melting width and power. There are display windows for laser control mode, reference track parameters, initial power setting, process power limit, pixel ratio, PID parameter setting, real-time melting curve window, real-time power curve, camera status, and laser status. The PC end is connected to the infrared camera junction box through the USB interface.

The technical method that the present invention adopts comprises the steps:

(1) Set the scanning speed, spot diameter, and powder feeding speed process parameters on the CNC platform of the laser directed energy deposition system, adjust the laser processing head to a suitable height above the processing platform, open the powder feeding channel and the gas feeding channel, and collect data on the PC side Set the initial laser power and laser control mode with the image processing system, and start printing;

(2) Set the laser control method of the PC-side integrated platform to manual, that is, there is no traditional deposition mode under the control of the PID algorithm, and record the real-time melting width value and power curve under the traditional mode through the data acquisition and image processing system;

(3) Set the laser control mode of the PC-side integrated platform to automatic, that is, the control mode that uses the PID algorithm for closed-loop control. Different reference value melting widths are respectively defined before and after the n-channels are deposited.

When depositing the first to nth channels, set the first melt pool width detected in the traditional mode as the reference value melting width, and compare the detected real-time melting width W _r (k) with the reference value melting width W _i (k) The difference e(k) is used as the input variable of the PID controller:

e(k)=W _i (k)-W _r (k);

Among them, W _i (k) is the reference value melting width, W _r (k) is the real-time melting width, and e(k) is the difference between the reference value melting width and the real-time melting width.

When depositing the n+1th pass, the average value of the melting width of the first n deposition layers is calculated, and the obtained average melting width is used as a new reference melting width.

f(k)= _Wn (k) _-Wr (k);

Among them, W _n (k) is the new reference value melting width after the nth channel deposition, n is the number of deposition channels, W _a (k) is the average melting width of each channel, and f(k) is the deposition value of the nth channel The difference between the new benchmark value of the fusing width and the real-time fusing width after the end.

(4) The difference between the reference melting width and the real-time melting width is used as the input of the PID controller, and the laser power is jointly regulated by three control components: proportional K _P , integral KI _, and differential K _D . The power change value before depositing n passes is set as:

The laser power after closed-loop control is:

The power change value after depositing n passes is set as:

The laser power after closed-loop control is:

Among them, K _p is the proportional control component, T _I is the integral constant in the integral control component, and T _D is the differential constant in the differential control component.

Set the variation of the real-time fusing width relative to the reference value fusing width as σ:

σ is the variation of the real-time molten pool width relative to the reference value. When the variation σ of the real-time molten pool width relative to the reference value is controlled within ±3%, it is considered to meet the control requirements.

(5) Based on the above algorithm formula, record the real-time melting width value and power curve under the control mode through the data acquisition and image processing system. After comparison, it is found that in the control mode, the variation σ of the melt width can be well controlled within ±3%, and the sag of the deposited sample is significantly improved.

Beneficial effects of the present invention: the device and method of the present invention use the PID algorithm to control the input of the laser melting rate in a closed loop, which significantly suppresses the accumulation of thermal effects and the continuous growth of the width of the molten pool, and effectively improves the problem of workpiece sagging. Accelerating the equiaxation of grains by improving the thermal gradient not only improves the cladding quality and material properties, but also prolongs the service life.

Description of drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings that are used in the examples or the description of the prior art.

Table 1 is the comparison of tensile strength and friction coefficient under the two modes.

Figure 1 is a closed-loop control laser power deposition manufacturing system.

Fig. 2 is a curve diagram of laser power and molten pool width in traditional mode.

Fig. 3 is a curve diagram of laser power and molten pool width in the control mode.

Figure 4 is the metallographic diagram of the side edge of the printed workpiece in the traditional mode and the control mode.

Figure 5 is the microstructure diagram under the traditional mode and the control mode.

In the above figure: 1: PC terminal; 2: powder feeder; 3: laser processing head; 4: infrared camera; 5: motion mechanism; 6: workpiece; 7: melting pool; 8: processing platform; 9: protective gas cylinder ; 10: water cooling protector; 11: laser source; 12: CNC platform.

Detailed ways

The specific implementation of the present invention will be described in detail below in conjunction with the accompanying drawings and examples, but the present invention should not be limited to the examples.

What this embodiment adopts is the 45 steel substrate of 150mm * 150mm * 10mm specification, cladding layer powder selects the nickel-chromium alloy (composition: 16-18wt% of chromium, 12-13wt% of nickel, 2-3wt of molybdenum) of grain size 50-150 μm %, silicon 0.8wt%, manganese 0.2wt%, carbon 0.03wt%, phosphorus 0.03wt%, sulfur 0.03wt%, oxygen 0.03wt%, iron 65-69wt%). EXAMPLES An experiment was carried out in Nanjing Zhongke Yuchen Laser Technology Co., Ltd., and a high-power laser energy directional deposition equipment model RC-LWD-6000 was selected, and the infrared camera model was CLAMAR.

First, a closed-loop control laser power laser directional deposition platform is built, which is composed of a laser directional energy deposition system, an online monitoring system for melting width, and a data acquisition and image processing system.

(1) Laser directed energy deposition system: The laser directed energy deposition system consists of a powder feeder 2, a laser processing head 3, a movement mechanism 5, a protective gas cylinder 9, a laser source 11, a water cooling protector 10, and a numerical control platform 12. The laser processing head 3 is connected to the numerical control platform 12 through the movement mechanism 5, and the parameters can be set by the numerical control platform 12 to make the laser processing head 3 move in XYZ three axes and multi-directionally. The laser processing head 3 integrates a powder feeding channel, an air feeding channel, an optical path and Water cooling pathway. The high-energy laser is generated in the laser source and transmitted to the generator through the optical fiber. After being focused by the combined optical mirror in the generator, the laser is emitted from the light exit hole of the nozzle of the laser processing head 3 and then focused on the substrate plane. The powder feeder 2, the shielding gas cylinder 9, and the water-cooling protector 10 are all electrically connected to the numerical control platform 12.

(2) Melting width online monitoring system: The body of the infrared camera 4 is equipped with an Ethernet connector, IO interface, SD memory card cover, water cooling interface, LED warning light, focusing mechanism optical device and head connection. The infrared camera junction box with multiple IO port cables is electrically connected to the power supply, and the infrared camera 4 is coaxially mounted on the laser processing head 3 through its head connection. Connect to the water-cooling protector 10 through the water-cooling interface, and use an Ethernet switch to connect to the PC terminal 1 through the Ethernet connector.

(3) Data acquisition and image processing system: The PC terminal 1 uses Labview to integrate the data acquisition and image processing system to realize online monitoring of melting width and power. There are display windows for laser control mode, reference track parameters, initial power setting, process power limit, pixel ratio, PID parameter setting, real-time melting curve window, real-time power curve, camera status, and laser status. PC terminal 1 is connected to the infrared camera junction box through the USB interface.

Closed-loop control of laser power The laser directional deposition platform was built for directional energy deposition experiments in the traditional mode. Set the laser process parameters: the scanning speed is 10mm/s, the powder feeding speed is 72g/min, the spot diameter is 4mm, the overlap rate is 50%, and the initial laser power is 2000W. Use a level to check the flatness of the substrate, open the powder feeding channel and the gas feeding channel, and check the smoothness of the powder and the amount of protective gas.

Example 1

Set the laser control mode to manual on the PC-side software control integration platform, click the record button, and the directed energy deposition equipment starts to work. The real-time melting curve and power are monitored and measured while deposition is being manufactured, and the drawn curve is shown in Figure 2.

Example 2

On the software control integration platform at the PC end, set the laser control mode to automatic, the reference track parameter to 3, the initial power setting to 2000W, the process power limit to the maximum value of 5000W, the minimum value to 500W, the pixel ratio to 0.333, the threshold value to 1025, and the PID parameter setting K _P : 200, K _I : 500, K _D : 100, camera status: connected, laser status: on, the number of single-layer deposition channels is 12, and the automatic learning number n of the control algorithm is set to 3.

When depositing the first to third passes, set the first molten pool width detected in the traditional mode as the reference value melting width, and compare the detected real-time melting width W _r (k) with the reference value melting width W _i (k) The difference e(k) is used as the input variable of the PID controller:

e(k)=W _i (k)-W _r (k);

Among them, W _i (k) is the reference value melting width, W _r (k) is the real-time melting width, and e(k) is the difference between the reference value melting width and the real-time melting width.

When depositing the fourth pass, the average value of the melt width of the first three deposition layers is calculated, and the obtained average melt width is used as the new benchmark melt width.

f(k)=W ₃ (k)-W _r (k);

Among them, W ₃ (k) is the new benchmark melting width after the third deposition, 3 is the number of depositions, W _a (k) is the average melting width of each deposition, f(k) is the third deposition The difference between the new benchmark value of the fusing width and the real-time fusing width after the end.

The difference between the reference melting width and the real-time melting width is used as the input of the PID controller, and the laser power is jointly regulated by three control components: proportional K _P , integral _KI , and differential K _D . The power change value before depositing 3 passes is set as:

The laser power after closed-loop control is:

The power change value after deposition of 3 passes is set as:

The laser power after closed-loop control is:

Among them, K _p is the proportional control component, T _I is the integral constant in the integral control component, and T _D is the differential constant in the differential control component.

Set the variation of the real-time fusing width relative to the reference value fusing width as σ:

σ is the variation of the real-time molten pool width relative to the reference value. When the variation σ of the real-time molten pool width relative to the reference value is controlled within ±3%, it is considered to meet the control requirements.

The real-time melting width value and power curve in the control mode are recorded through the data acquisition and image processing system. After comparison, it is found that in the control mode, the variation σ of the melt width can be well controlled within ±3%, and the sag of the deposited sample is significantly improved.

Click the record button, and the directed energy deposition equipment starts to work. The real-time melting width curve and laser power curve are monitored during deposition manufacturing, and the drawn curve is shown in Figure 3. When the variation σ of the real-time melting width relative to the reference value melting width is controlled within ±3%, it is considered to meet the control requirements. Tensile tests and wear tests were performed on workpieces formed in both modes.

From the comparison of the melt pool width and laser power curves in the two modes of Figure 2 and Figure 3, it can be seen that the traditional mode is deposited at a constant 2000W, due to the heat accumulation effect caused by the slow cooling rate, the melt width during the deposition process Gradually increase from 2.26mm to 2.6mm. It can be seen from the sectional view a of the first wall-shaped workpiece in Figure 4 that significant collapse occurs on both sides of the molding. In the control mode, the equipment performs deposition and manufacturing with dynamically reduced power. In the first three passes of the algorithm's self-learning, the laser power remains unchanged at 2000W. From the fourth pass of deposition, the power is slowly reduced from 2000W to ~1880W, and the width of the final molten pool The overall is basically stable at 2.26 mm. It can be seen from the sectional view b of the second wall-shaped workpiece in Fig. 4 that the collapse phenomenon on both sides of the molded part has been significantly improved. It can also be seen from the microstructure comparison diagram of Fig. 5 that the grain size in the control mode in Fig. 5b is smaller than that in the conventional mode in Fig. 5a. By controlling the heat input in a closed loop, the thermal gradient can be significantly improved, thereby refining the grains and accelerating the formation of equiaxed grains.

Table 1 is the comparison of tensile strength and wear coefficient under the two modes. It can be seen that the tensile strength in the control mode has been significantly improved compared with the traditional mode, with a maximum increase of 64.2%. In the control mode, the friction coefficient and wear amount are also significantly reduced, which represents the improvement of wear resistance. Combined with the experimental results of workpiece forming conditions, tensile properties and wear properties, using PID algorithm to control laser power in a closed loop can effectively improve workpiece forming quality and mechanical properties.

Table 1

serial number	Tensile strength/MPa	coefficient of friction	Abrasion/g
1-1 (Example 1)	670	0.60	2.0
1-2 (Example 1)	710	0.58	1.8
1-3 (Example 1)	685	0.60	2.0
2-1 (Example 2)	1070	0.48	0.9
2-2 (Example 2)	1056	0.45	0.8
2-3 (Example 2)	1100	0.45	0.8

Claims (5)

1. A device for closed-loop control of laser power to improve the problem of workpiece sagging, the device includes a laser directed energy deposition system, characterized in that the device also includes an online monitoring system for melting width and a data acquisition and image processing system, online monitoring of melting width The system includes an infrared camera. The infrared camera body is equipped with an Ethernet connector, IO interface, SD memory card cover, water cooling interface, LED warning light, focusing mechanism optical device and head connection; an infrared camera junction box with multiple IO port cables Electrically connect to the power supply, install the infrared camera coaxially on the laser processing head through its head, connect to the water-cooling protector through the water-cooling interface, and use the Ethernet switch to connect to the PC through the Ethernet connector; data acquisition and image processing The system includes a PC terminal, which uses Labview to integrate data acquisition and image processing systems to realize online monitoring of melting width and power. It is equipped with laser control mode, reference track parameters, initial power setting, process power limit, pixel ratio, PID Parameter setting, real-time melting curve window, real-time power curve, camera status, laser status display window, the PC end is connected to the infrared camera junction box through the USB interface.
2. A device for improving workpiece slump by closed-loop control of laser power as claimed in claim 1, characterized in that the laser directed energy deposition system consists of a laser source, a water-cooled protector, a numerical control platform, a powder feeder, and a protective gas cylinder , laser processing head, and motion mechanism; the laser processing head is connected to the CNC platform through the motion mechanism, and the parameters are set by the CNC platform to make the laser processing head move in XYZ three-axis multi-directional movement. The laser processing head integrates powder feeding passage, air supply passage, Optical path and water-cooling path; high-energy laser is generated in the laser source, then emitted from the light exit hole of the laser processing head nozzle, and then focused on the substrate plane; the powder feeder, protective gas cylinder, and water-cooled protector are all electrically connected to the CNC platform.
3. A method for closed-loop control of laser power to improve workpiece sag, characterized in that the specific steps are as follows:

   (1) Set the scanning speed, spot diameter, and powder feeding speed process parameters on the CNC platform of the laser directed energy deposition system, adjust the laser processing head to a suitable height above the processing platform, open the powder feeding channel and the gas feeding channel, and collect data on the PC side Set the initial laser power and laser control mode with the image processing system, and start printing;

   (2) Set the laser control method of the PC-side integrated platform to manual, that is, there is no traditional deposition mode under the control of the PID algorithm, and record the real-time melting width value and power curve under the traditional mode through the data acquisition and image processing system;

   (3) Set the laser control mode of the PC-side integrated platform to automatic, that is, use the PID algorithm to perform closed-loop control control mode, and define different reference value melting widths before and after n-pass deposition;

   (4) The difference between the reference melting width and the real-time melting width is used as the input of the PID controller, and the laser power is jointly regulated by the three control components of the proportional K _P , the integral _KI , and the differential K _D. The power change before depositing n channels The value is set to:

   

   The laser power after closed-loop control is:

   

   The power change value after depositing n passes is set as:

   

   The laser power after closed-loop control is:

   

   Among them, _Kp is the proportional control component, T _I is the integral constant in the integral control component, and T _D is the differential constant in the differential control component;

   Set the variation of the real-time fusing width relative to the reference value fusing width as σ:

   

   σ is the variation of the real-time molten pool width relative to the reference value. When the variation σ of the real-time molten pool width relative to the reference value is controlled within ±3%, it is considered to meet the control requirements.
4. The method according to claim 3, characterized in that, the specific steps of defining different reference value melting widths respectively before depositing n-passes and after depositing n-passes are:

   When depositing the first to nth channels, set the first melt pool width detected in the traditional mode as the reference value melting width, and compare the detected real-time melting width W _r (k) with the reference value melting width W _i (k) The difference e(k) is used as the input variable of the PID controller:

   e(k)=W _i (k)-W _r (k);

   Among them, W _i (k) is the reference value melting width, W _r (k) is the real-time melting width, e(k) is the difference between the reference value melting width and the real-time melting width;

   When depositing the n+1th pass, the average value of the melting width of the first n deposition layers is calculated, and the obtained average melting width is used as the new benchmark melting width;

   

   f(k)= _Wn (k) _-Wr (k);

   Among them, W _n (k) is the new reference value melting width after the nth channel deposition, n is the number of deposition channels, W _a (k) is the average melting width of each channel, and f(k) is the deposition value of the nth channel The difference between the new benchmark value of the fusing width and the real-time fusing width after the end.
5. The method according to claim 3 or 4, characterized in that, the range of n is 1/4 to 1/3 of the total number of single-layer deposition.

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