On-line regulation and control method for light spot diameter of variable-thickness titanium alloy curved surface component

Abstract

The invention discloses an online regulation and control method for the light spot diameter of a variable-thickness titanium alloy curved surface component, and relates to the field of laser molten pool quality monitoring research. Processing the metal powder by using laser according to the three-dimensional modeling; a CCD (Charge Coupled Device) camera in the real-time monitoring system acquires a molten pool image in the vertical direction, and a data acquisition and image processing system performs processing according to the molten pool image acquired by the real-time monitoring system and data of a double-colorimetric infrared thermometer so as to judge the thicknesses of different positions of a workpiece to be processed; and the laser directional energy deposition system adjusts the laser spot diameter to process the workpiece according to the thicknesses of different positions of the workpiece to be processed, which are judged by the data acquisition and image processing system. The problem that the larger the curvature of the laser deposition curved surface structure is, the thicker the workpiece is is solved, and the uniformity of the thickness of the workpiece of the laser deposition curved surface structure is improved.

Description

Technical Field

[0001] The invention relates to the research field of laser molten pool quality monitoring, and in particular to an online control method for the spot diameter of a titanium alloy curved surface component with variable thickness. Background Art

[0002] Laser directed energy deposition technology is an emerging processing technology developed in the mid-1980s. Laser directed energy deposition can be applied to the additive manufacturing of titanium alloys, aluminum alloys, nickel alloys, high entropy alloys, stainless steel, carbon steel and other materials; it can be used for various processing processes such as laser repair of parts and laser 3D printer alloying; it can be expanded to four-axis or five-axis machine tools, suitable for rapid prototyping of various large and complex parts, and is mostly used in the aerospace field such as engine blade repair, shaft parts repair, etc.

[0003] Laser directed energy deposition deposition equipment emits a high-energy laser beam through a nozzle. The laser beam melts the metal powder into a molten pool, and the required components are obtained through layer-by-layer accumulation and repair. Laser deposition technology can simplify the processing process, shorten the processing cycle, and reduce production costs. Laser deposition technology provides new solutions for the development of manufacturing. Laser directed energy deposition equipment uses a CCD camera to collect images and adopts infrared imaging technology. The infrared lens receives the infrared radiation reflected by the object and generates an infrared thermal image through the detector after circuit processing. The advantages of CCD cameras include lightness and convenience, non-destructive testing, strong anti-interference, and high clarity. Using CCD cameras to detect the molten pool area greatly improves manufacturing efficiency. Among them, in deposition manufacturing, there will be a problem that the thickness of the workpiece will be thicker where the curvature is greater, which seriously affects the surface quality and mechanical properties of the workpiece. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides an online control method for the spot diameter of a titanium alloy curved surface component with variable thickness. During the laser cladding process, a coaxial CCD camera is used to obtain a vertical molten pool image to achieve the purpose of real-time monitoring of the width of the molten pool. A dual-color infrared thermometer is used to receive the thermal feedback transmitted by the workpiece to obtain a thermal image of the workpiece and determine the thickness of the workpiece at different positions. The detected value is used as the input variable of the PID controller, and the laser power is jointly controlled by the three control components of proportion, differentiation and integration, and then fed back to the laser directional energy deposition system; this method effectively controls the size of the laser emitted by the high-energy laser beam by adjusting the spot diameter of the laser processing head, which can significantly improve the problem that the thickness of the workpiece is thicker where the curvature is greater, and improve the uniformity of the thickness of the workpiece of the laser deposited curved surface structure.

[0005] The present invention achieves the above technical objectives through the following technical means.

[0006] A method for online control of the spot diameter of a titanium alloy curved surface component with variable thickness comprises the following steps:

[0007] Carry out 3D modeling of the workpiece to be processed;

[0008] Processing metal powders using lasers based on 3D modeling;

[0009] The CCD camera in the real-time monitoring system acquires the vertical molten pool image.

[0010] The data acquisition and image processing system processes the molten pool image collected by the real-time monitoring system and the data of the dual-color infrared thermometer to determine the thickness of different positions of the workpiece to be processed;

[0011] The laser directed energy deposition system adjusts the laser spot diameter to process the workpiece according to the thickness of different positions of the workpiece to be processed determined by the data acquisition and image processing system.

[0012] In the above scheme, the laser spot diameter is adjusted by using the PID closed-loop control method, using the relationship between proportion, differential and integral to jointly control the laser spot diameter:

[0013] Real-time workpiece thickness W r (k) and reference workpiece thickness W i The difference e(k) between (k) and (k) is used as the input variable of the PID controller: e(k) = W i (k)-W r (k);

[0014] Take e(k) as the input of PID controller and adjust it by proportional K p , integral T I and differential T D The three control components jointly regulate the laser power to change the laser spot diameter, and the change value of the laser power is set to:

[0015]

[0016] The laser power after closed-loop control is:

[0017]

[0018] Among them, K p is the proportional control component, T I is the integral constant in the integral control component, T D is the differential constant in the differential control variable.

[0019] In the above scheme, in the laser directed energy deposition system, the laser processing head is connected to the CNC platform through a motion mechanism, and the CNC platform sets parameters to enable the laser processing head to perform three-axis multi-directional motion; the laser beam emitted by the laser source melts the metal powder into a molten pool, and the desired workpiece is obtained through layer-by-layer accumulation and repair.

[0020] In the above scheme, the laser directed energy deposition system includes a PC end, a water-cooled protector, a protective gas cylinder, a laser source, a CNC platform and a powder feeder; the powder feeder, the protective gas cylinder and the water-cooled protector are connected to the CNC platform through wires; and the CNC platform is connected to the PC end.

[0021] In the above scheme, the laser control mode, reference orbit parameters, initial power setting, process power limit, pixel ratio, PID parameter setting, real-time power curve, camera status and laser status display window are set on the PC side.

[0022] In the above solution, the CCD camera is installed on the laser processing head.

[0023] In the above scheme, the data acquisition and image processing system uses machine vision software on the PC side to collect images captured by the CCD camera, and at the same time collects the thermal imaging image transmitted by the workpiece received by the dual-colorimetric infrared thermometer. It is equipped with image variables, control variables, input and output operator functions, image preprocessing, grayscale processing, image segmentation, character recognition, and analog-to-digital conversion, so as to determine the thickness of the workpiece at different positions.

[0024] In the above scheme, the real-time monitoring system includes a CCD camera and a dual-colorimetric infrared thermometer.

[0025] In the above scheme, the dual-color infrared thermometer shown is a handheld device used to monitor the temperature changes of the workpiece during the processing.

[0026] Beneficial effects:

[0027] 1. The method of the present invention uses a PID algorithm to close the spot diameter of the laser processing head, so that the thickness of the curved surface structure with a large curvature becomes thinner and equal to the thickness of the curved surface structure with a small curvature. This improves the problem that the thickness of the workpiece is thicker where the curvature of the laser deposited curved surface structure is larger, and improves the uniformity of the thickness of the workpiece of the laser deposited curved surface structure.

[0028] 2. In the laser cladding process, the present invention uses a coaxial CCD camera to obtain a vertical molten pool image to achieve the purpose of real-time monitoring of the width of the molten pool, and uses a dual-color infrared thermometer to receive the thermal feedback transmitted by the workpiece to obtain a thermal image of the workpiece, and judge the thickness of the workpiece at different positions. The detected value is used as the input variable of the PID controller, and the laser power is jointly regulated by the three control components of proportion, differentiation, and integration, and then fed back to the laser directional energy deposition system; this method effectively controls the size of the laser emitted by the high-energy laser beam by regulating the spot diameter of the laser processing head, which can significantly improve the problem that the thickness of the workpiece is thicker in places with greater curvature, and improve the uniformity of the thickness of the workpiece with a laser-deposited curved surface structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the on-line control device for the spot diameter of a titanium alloy curved surface component with variable thickness;

[0030] Figure 2 A schematic diagram of a component structure obtained without using the method of the present invention;

[0031] Figure 3 A schematic diagram of a component structure obtained by the method of the present invention;

[0032] Figure 4 The figure is a schematic diagram of an integral blade of an aircraft compressor obtained by using the method of the present invention.

[0033] Reference numerals:

[0034] 1-PC terminal; 2-powder feeder; 3-laser processing head; 4-CCD camera; 5-dual colorimetric infrared thermometer: 6-motion mechanism; 7-workpiece; 8-molten pool; 9-processing platform; 10-protective gas cylinder; 11-water cooling protector; 12-laser source; 13-CNC platform. DETAILED DESCRIPTION

[0035] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0036] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "axial", "radial", "vertical", "horizontal", "inner", "outer" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.

[0037] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0038] This embodiment uses a 45 steel substrate with a specification of 150mm×150mm×10mm, and the cladding layer powder is selected from Ti6Al4V titanium alloy (composition: titanium (Ti) balance, nitrogen (N) ≤0.05, carbon (C) ≤0.08, hydrogen (H) ≤0.015, iron (Fe) ≤0.40, oxygen (O) ≤0.20, aluminum (Al) (5.5-6.75) and vanadium (V) 3.5-4.5).

[0039] The laser directed energy deposition system includes a powder feeder 2, a laser processing head 3, a motion mechanism 6, a protective gas cylinder 10, a laser source 12, a water-cooled protector 11, and a numerical control platform 13; the laser processing head 3 is connected to the numerical control platform 13 through the motion mechanism 6, and the numerical control platform 13 sets parameters to make the laser processing head 3 move in three axes and in multiple directions. The laser source emits a high-energy laser, and the high-energy laser beam is emitted through the nozzle, and the required components are manufactured by focusing on the substrate plane. The powder feeder 2, the protective gas cylinder 10, and the water-cooled protector 11 are all electrically connected to the numerical control platform 13.

[0040] In the real-time monitoring system, the CCD camera 4 body is provided with an Ethernet connector, an IO interface, an SD memory card cover, a water cooling interface, an LED display light, a focusing mechanism optical device and a head connection. The infrared camera 4 junction box with a multi-IO port cable is electrically connected to the power supply, and the CCD camera 4 is installed on the laser processing head 3 to obtain a vertical molten pool image, so as to achieve the purpose of real-time monitoring of the width of the molten pool. In addition, a dual-color infrared thermometer 5 is installed to receive the thermal feedback transmitted by the workpiece to obtain a thermal image of the workpiece, so as to determine the thickness of the workpiece at different positions. It is connected to the water cooling protector through the water cooling interface, and connected to the PC terminal 1 through the Ethernet connector using an Ethernet switch.

[0041] Data acquisition and image processing system: The data acquisition system is integrated with software on the PC end 1 to realize online monitoring of the spot diameter of the laser processing head 3. Display windows for laser control mode, reference track parameters, initial power setting, process power limit, pixel ratio, PID parameter setting, real-time power curve, camera status, and laser status are set. The PC end 1 is connected to the CCD camera 4 junction box via a USB interface; the machine vision software is used on the PC end 1 to collect the images captured by the CCD camera 4, and at the same time, the thermal imaging image transmitted by the workpiece received by the dual colorimetric infrared thermometer 5 is collected, and image variables, control variables, input and output operator functions, image preprocessing, grayscale processing, image segmentation, character recognition, and analog-to-digital conversion are set. In this way, the thickness of the workpiece at different positions can be determined.

[0042] The platform was built using a laser directional energy deposition system, and the spot diameter was changed using the PID closed-loop control method. The laser deposition parameters were set as follows: scanning speed of 600 mm / min, powder feeding speed of 1 rad, and laser power of 1800 W. The initial spot diameter was 4 mm.

[0043] Place the substrate on the operating table and use a level to check the flatness of the substrate, open the powder feeding passage and the gas feeding passage, and check the smoothness of the metal powder and the remaining amount of protective gas. Check whether the moving components, molten pool, infrared camera and other parts can operate normally. After the preparation work is completed, deposition manufacturing begins. Set the laser deposition process parameters on the PC side: the reference track parameter is 3, the initial spot diameter is set to 4mm, and the process spot diameter limit is a maximum of 6mm and a minimum of 1mm. The spot diameter of the laser processing head is achieved by changing the laser power using PID control. Therefore, set the PID control parameters, connect the CCD camera and the dual-colorimetric infrared thermometer, turn on the laser processing head, click the "Start" button on the PC system control interface, and the laser directional energy deposition equipment starts working. The number of single-layer deposition passes is 16 layers.

[0044] The real-time workpiece thickness W r (k) and reference workpiece thickness W iThe difference e(k) between (k) and (k) is used as the input variable of the PID controller: e(k) = W i (k)-W r (k). Taking e(k) as the input of the PID controller, the laser power is regulated by controlling the components to achieve the purpose of changing the spot diameter of the laser processing head. The change value of the laser power is set as:

[0045]

[0046] The laser power after closed-loop control is:

[0047]

[0048] Input the component curvature data set on the PC, plan the operation trajectory of the laser processing head, and set different spot diameters according to different curvatures.

[0049] Specifically, the initial laser power is set to 1800w in the PC software control system, the laser power parameter is set to 1000w-3000w, and the PID control parameters are Kp=50, Ti=200, Td=0.05. When the number of deposition layers is 1, assuming that the real-time workpiece thickness is 4mm and the reference workpiece thickness is 2mm, the input variable e(k) of the PID controller is -2, and the power change value is -100.6w. At this time, the laser power after closed-loop control is 1699.4w.

[0050] Figure 2 , Figure 3 and Figure 4 It is a simulation diagram drawn by software. Figure 2 It can be seen that the thickness of the component is different at different curvatures, and after PID closed-loop control, Figure 3 As shown, the manufactured component improves this problem and realizes uniform thickness. This shows that the method of the present invention can significantly improve the problem that the thickness of the workpiece is thicker where the curvature is greater by adjusting the spot diameter of the laser processing head and effectively controlling the size of the laser emitted by the high-energy laser beam, thereby improving the uniformity of the thickness of the workpiece of the laser deposited curved surface structure. Figure 4 is based on Figure 3 The complex components drawn on this basis can be used in the blades of aircraft engine compressors in the aerospace field.

[0051] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0052] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and intent of the present invention.

Claims

1. A method for online control of the spot diameter of a titanium alloy curved surface component with variable thickness, characterized in that: The steps include: Carry out 3D modeling of the workpiece to be processed; Processing metal powders using lasers based on 3D modeling; The CCD camera in the real-time monitoring system acquires the vertical molten pool image. The data acquisition and image processing system processes the molten pool image collected by the real-time monitoring system and the data of the dual-color infrared thermometer to determine the thickness of different positions of the workpiece to be processed; The laser directed energy deposition system adjusts the laser spot diameter to process the workpiece according to the thickness of different positions of the workpiece to be processed determined by the data acquisition and image processing system.

2. The method for online control of the spot diameter of a titanium alloy curved surface component with variable thickness according to claim 1 is characterized in that: The laser spot diameter is adjusted by using the PID closed-loop control method, using the relationship between proportion, differential and integral to jointly control the laser spot diameter: Real-time workpiece thickness W r (k) and reference workpiece thickness W i The difference e(k) between (k) and (k) is used as the input variable of the PID controller: e(k) = W i (k)-W r (k); Take e(k) as the input of PID controller and adjust it by proportional K p , integral T I and differential T D The three control components jointly regulate the laser power to change the laser spot diameter, and the change value of the laser power is set to: 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, T D is the differential constant in the differential control variable.

3. The method for online control of the spot diameter of a titanium alloy curved surface component with variable thickness according to claim 1 is characterized in that: In the laser directed energy deposition system, a laser processing head is connected to a numerical control platform via a motion mechanism, and the numerical control platform sets parameters to enable the laser processing head to perform three-axis multi-directional motion; the laser beam emitted by the laser source melts the metal powder into a molten pool, and the desired workpiece is obtained through layer-by-layer accumulation and repair.

4. The method for online control of the spot diameter of a titanium alloy curved surface component with variable thickness according to claim 3 is characterized in that: The laser directed energy deposition system comprises a PC terminal, a water-cooled protector, a protective gas cylinder, a laser source, a numerical control platform and a powder feeder; the powder feeder, the protective gas cylinder and the water-cooled protector are connected to the numerical control platform through wires; and the numerical control platform is connected to the PC terminal.

5. The method for online control of the spot diameter of a titanium alloy curved surface component with variable thickness according to claim 4 is characterized in that: The laser control mode, reference track parameters, initial power settings, process power limits, pixel ratios, PID parameter settings, real-time power curves, camera status, and laser status display windows are set on the PC.

6. The method for online control of the spot diameter of a titanium alloy curved surface component with variable thickness according to claim 3 is characterized in that: The CCD camera is installed on the laser processing head.

7. The method for online control of the spot diameter of a titanium alloy curved surface component with variable thickness according to claim 1, characterized in that: The data acquisition and image processing system uses machine vision software on the PC to collect images captured by the CCD camera, and at the same time collects the thermal imaging image transmitted by the workpiece received by the dual-color infrared thermometer. It is equipped with image variables, control variables, input and output operator functions, image preprocessing, grayscale processing, image segmentation, character recognition, and analog-to-digital conversion, so as to determine the thickness of the workpiece at different positions.

8. The method for online control of the spot diameter of a titanium alloy curved surface component with variable thickness according to claim 1, characterized in that: The real-time monitoring system includes a CCD camera and a dual-color infrared thermometer.

9. The method for online control of the spot diameter of a titanium alloy curved surface component with variable thickness according to claim 1, characterized in that: The dual-color infrared thermometer shown is a handheld device used to monitor the temperature changes of workpieces during processing.

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