Estimation method and device for steam eruption impact behavior in laser-induced keyhole

Abstract

The invention provides a method and device for estimating the steam eruption impact behavior in a laser-induced keyhole, and belongs to the technical field of laser material processing.The method comprises the steps that a metal molten drop is arranged above the laser-induced keyhole, and a high-speed camera is used for shooting a transition image of the metal molten drop above the keyhole; obtaining a relation curve of the flight speed of the metal droplet along with time change through image analysis, and obtaining the position when the resultant force is zero; stress analysis is conducted on the metal molten drops with the resultant force being zero; and the jet steam impact force borne by the metal molten drops at the position is obtained through the static equilibrium theory. By adopting the method and the device for estimating the impact behavior of the steam eruption in the laser-induced keyhole, the specific numerical value of the pressure of the steam eruption in the high-power laser-induced keyhole can be estimated, and the research on laser-induced metal steam is facilitated. The experimental method is simple and easy to implement, small in calculation amount and suitable for measuring the pressure of the steam erupted in the laser-induced keyhole of various metal materials under different machining conditions.

Description

Technical Field

[0001] The invention relates to the technical field of laser material processing, and in particular to a method and a device for estimating impact behavior of steam eruption in a keyhole caused by laser. Background Art

[0002] Laser processing technology, as an advanced processing method that has rapidly emerged in recent decades, has shown great potential in many key industrial fields such as automobile and shipbuilding, power battery industry, aerospace, etc., with its low heat input, high precision, large aspect ratio processing capabilities and highly automated characteristics. In recent years, the vigorous development of domestic lasers has effectively reduced equipment costs, promoted the widespread application of laser processing technology in the civilian field, and gradually established its core position in the modern processing technology system.

[0003] However, the metal vapor problem accompanying high-power laser processing cannot be ignored. The laser beam acts on the surface of the material, inducing rapid melting and evaporation of the metal to form a keyhole structure. As the processing progresses, the liquid metal on the front wall of the keyhole quickly vaporizes to produce high-pressure steam. This steam dynamic will not only cause violent fluctuations in the molten pool on the back wall of the keyhole, affecting the processing stability, but also carry molten metal to form splashes, posing a threat to processing quality and equipment safety. In laser-arc hybrid processing, the impact of high-pressure metal vapor on the metal droplets further hinders the smooth transition of the metal droplets and reduces processing efficiency.

[0004] In response to the above problems, the present invention proposes an innovative estimation method and device, which aims to accurately quantify the impact behavior of laser-induced metal vapor eruption in the keyhole. This method combines the force analysis of flying metal droplets in laser-arc composite manufacturing with high-speed camera technology. By capturing the image of the motion trajectory of the metal droplet, the critical point where the resultant force on the metal droplet is zero is accurately identified, and on this basis, the static equilibrium principle is used to calculate the metal vapor eruption impact force on the metal droplet. This method not only realizes the accurate quantification of the impact behavior of metal vapor eruption, but also provides a scientific basis for optimizing the stability of the laser processing process, improving the design of metal vapor protection devices and purge gas, and fine-tuning the process parameters of laser and laser-arc composite manufacturing. Summary of the invention

[0005] The purpose of the present invention is to provide a method and device for estimating the impact behavior of steam eruption in a laser keyhole, which is suitable for studying the characteristic behavior of metal vapor erupting in a laser keyhole in the fields of laser welding, laser-arc hybrid welding, etc.

[0006] To achieve the above object, the present invention provides a method for estimating the impact behavior of laser-induced steam eruption in a keyhole, comprising the following steps:

[0007] Step S1, adding a metal droplet above the laser keyhole by means of MIG or TIG arc, obtaining the coordinates of the center of mass of the metal droplet in each frame within a flight cycle by using a high-speed camera, calculating the average speed of each time period, and obtaining a curve of the change of the flight speed of the metal droplet over time. When the slope of the change curve is zero, the position and time at which the resultant force on the metal droplet is zero are obtained;

[0008] Step S2, using a high-speed camera to obtain the morphological parameters of the metal droplet in a flight cycle, and calculating the plasma flow force and gravity on the metal droplet at a point where the resultant force on the metal droplet is zero according to the relationship between the current and the flight distance of the metal droplet;

[0009] Step S3, according to the static equilibrium theory, the deceleration force on the metal droplet at the point where the resultant force is zero is calculated, that is, the impact pressure exerted on the metal droplet by the steam ejected in the keyhole caused by the laser at this point.

[0010] Preferably, in step S1, the average speed in each time period is calculated as follows:

[0011]

[0012] Among them, S i x is the length of the metal droplet flying during the interval between two adjacent frames; i-1 ,y i-1 is the coordinate of the center of mass of the metal droplet in the previous frame; x i ,y i is the coordinate of the center of mass of the metal droplet in the next frame; t is the time interval between two adjacent frames; v i is the average speed in each time period.

[0013] Preferably, in step S2, the plasma flow force on the metal droplet is calculated as follows:

[0014]

[0015] Among them, F P is the plasma flow force on the metal droplet; C d is the plasma flow coefficient; A is the cross-sectional area of ​​the metal droplet along the axis of the welding wire; ρ f is the plasma density; v f is the plasma flow rate;

[0016] ρ f The calculation formula is as follows:

[0017]

[0018] Wherein, P is standard atmospheric pressure; R is gas constant; M is molar mass of shielding gas; T is arc temperature;

[0019] v f The calculation formula is as follows:

[0020] v f = kI(5);

[0021] Where k is a constant; I is the plasma current at the location of the metal droplet, and the calculation formula of I is as follows:

[0022] I=I0e -zd (6);

[0023] Where I0 is the arc current when the metal droplet just separates; z is a constant; d is the flying distance of the metal droplet;

[0024] C d The calculation formula is as follows:

[0025]

[0026] Where Re is the plasma Reynolds number, and the calculation formula of Re is as follows:

[0027]

[0028] Wherein, μ is the viscosity coefficient of the high temperature protective gas; D is the average diameter of the metal droplet, and the calculation formula of D is as follows:

[0029]

[0030] Among them, h and w are the major axis and minor axis of the metal droplet, respectively.

[0031] Preferably, in step S2, the gravity exerted on the metal droplet is calculated by the following formula:

[0032] F G =ρ d Vg (10);

[0033] Among them, F G is the gravity on the metal droplet; ρ d is the density of the metal droplet; g is the acceleration of gravity; V is the average volume of the metal droplet, and the calculation formula of V is as follows:

[0034]

[0035] Preferably, in step S3, the deceleration force on the metal droplet at the point where the resultant force is zero is calculated as follows:

[0036] F m =F G +F P (12);

[0037] Among them, F m For deceleration force.

[0038] Based on the above-mentioned method for estimating the impact behavior of steam eruption in a laser-induced keyhole, the present invention also provides a device for estimating the impact behavior of steam eruption in a laser-induced keyhole, comprising a workpiece to be welded, a high-power laser is arranged on the upper side of the workpiece to be welded, the high-power laser emits a laser beam perpendicular to the workpiece to be welded, a welding gun is arranged on one side of the intersection of the laser beam and the workpiece to be welded, semiconductor lighting lasers and high-speed cameras are symmetrically placed on both sides of the laser beam, the semiconductor lighting laser is connected to the semiconductor lighting laser power supply, and the high-speed camera is connected to a computer.

[0039] Among them, a high-power laser is used to generate a laser beam and act on the welding area to form a keyhole;

[0040] The welding gun is any one of a MIG welding gun and a TIG welding gun, which is arranged near the high-power laser and is used to heat the welding wire and generate metal droplets;

[0041] Semiconductor illumination laser and semiconductor illumination laser power supply, used to provide background illumination light to illuminate the flight process of metal molten droplets;

[0042] A high-speed camera, equipped with a narrow-band filter, is placed perpendicular to the laser scanning direction and symmetrically with the semiconductor illumination laser to capture the transition image of the metal droplet above the keyhole;

[0043] A computer is used to receive and process image data captured by a high-speed camera.

[0044] Preferably, the high-power laser is any one of a fiber laser, a Nd:YAG laser, a CO2 laser, a blue laser, a green laser or a semiconductor laser, and the laser output power is 0.5 to 50 kW.

[0045] Preferably, the angle between the laser beam emitted by the high-power laser and the welding wire is 0 to 80°; the distance between the laser focus point and the tip of the welding wire is -2 to 5 mm.

[0046] Preferably, the shooting frame rate of the high-speed camera is 1000-50000 frames / s, and a narrow-band filter having a central band consistent with the wavelength of the illumination light of the semiconductor illumination laser is arranged in front of the lens of the high-speed camera.

[0047] Preferably, the wavelength band of the illumination light of the semiconductor illumination laser is 400-900 nm, and the laser output power is 0.01-50 W.

[0048] Therefore, the present invention adopts the above-mentioned method and device for estimating the impact behavior of steam eruption in a keyhole induced by laser, and the beneficial technical effects are as follows:

[0049] (1) Accurately estimate the impact force of steam eruption: The present invention uses a high-speed camera to capture the transition image of the metal droplet above the keyhole, and uses image analysis to obtain the relationship between the flight speed of the metal droplet and time. Furthermore, by analyzing the force of the metal droplet at the point where the resultant force is zero, the impact pressure exerted on the metal droplet by the steam erupting in the keyhole caused by the laser can be accurately estimated. This technology provides a powerful tool for studying steam behavior in the field of laser material processing.

[0050] (2) The experimental method is simple and easy: The estimation method of the present invention mainly relies on high-speed camera technology, and the experimental equipment is relatively simple and easy to operate. At the same time, due to the small amount of calculation, the method has high efficiency and feasibility in practical application.

[0051] (3) Wide applicability: The present invention is not only applicable to the field of laser welding, but can also be widely used in the research of laser-arc hybrid welding and other fields involving the impact behavior of laser-induced steam eruption in keyholes. In addition, the method is also applicable to the measurement of steam pressure of various metal materials under different processing conditions, and has high versatility and practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 It is a schematic structural diagram of a device for estimating the impact behavior of laser-induced steam eruption in a keyhole according to the present invention;

[0053] Figure 2 This is a binary image of a metal droplet flying during a transition period obtained in the experiment;

[0054] Figure 3 It is a schematic diagram of the force analysis of a flying metal droplet;

[0055] Figure 4 This is the curve of the relationship between the flying speed of the molten metal droplet and time in a transition period obtained in the experiment.

[0056] Reference numerals

[0057] 1. High-power laser; 2. Welding gun; 3. Workpiece to be welded; 4. Semiconductor lighting laser; 5. Semiconductor lighting laser power supply; 6. High-speed camera; 7. Narrow-band filter; 8. Computer; 9. Welding wire; 10. Metal droplet; 11. Arc plasma; 12. Metal vapor; 13. Keyhole; 14. The point where the resultant force starts to be zero. DETAILED DESCRIPTION

[0058] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0059] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0060] Embodiment 1

[0061] like Figure 1 As shown, the present invention provides an estimation device for the impact behavior of steam eruption in a keyhole induced by a laser, comprising a workpiece 3 to be welded, a high-power laser 1 is arranged on the upper side of the workpiece 3 to be welded, the high-power laser 1 emits a laser beam perpendicular to the workpiece 3 to be welded, a welding gun 2 is arranged on one side of the intersection of the laser beam and the workpiece 3 to be welded, semiconductor lighting lasers 4 and high-speed cameras 6 are symmetrically placed on both sides of the laser beam, the semiconductor lighting laser 4 is connected to a semiconductor lighting laser power supply 5, and the high-speed camera 6 is connected to a computer 8.

[0062] The high-power laser 1 is used to generate a laser beam and act on the workpiece 3 to be welded to form a keyhole. In this embodiment, the high-power laser 1 is an IPG YLS-6000 fiber laser with a laser wavelength of 1070 nm.

[0063] The welding gun 2 is any one of a MIG welding gun and a TIG welding gun, which is arranged near the collimation head of the high-power laser 1, and is used to heat the welding wire 9 and generate metal droplets; in this embodiment, a MIG welding machine is used, the MIG welding machine is a Fronius TS 5000, and the wire feeder is a Fronius VR 4000. The workpiece 3 to be welded is Q235 low-carbon steel, with a size of 100mm×50mm×10mm, the welding wire 9 used is an ER308LSi stainless steel welding wire with a diameter of 1mm, and the shielding gas is 99.99% pure argon. The composite welding parameters are: laser-guided welding, defocusing amount 0mm, welding speed 1.2m / min, shielding gas flow rate 17L / min, welding wire dry extension 15mm, light wire spacing 3mm, heat source angle 45°, laser power 6kW, welding current 260A, and metal droplet transition mode is jet transition.

[0064] The semiconductor illumination laser 4 and the semiconductor illumination laser power supply 5 are used to provide background illumination light to illuminate the flight process of the metal droplet; the semiconductor illumination laser 4 uses the Keplin K808DA5RN-50W fiber-coupled semiconductor laser, and the illumination laser wavelength is 808nm.

[0065] A narrowband filter 7 with a central band of 808 nm is arranged in front of the lens of the high-speed camera 6. The high-speed camera 6 is perpendicular to the laser scanning direction and symmetrically placed with the semiconductor illumination laser 4 to capture the transition image of the metal droplet above the keyhole. The high-speed camera 6 uses the American PHOTRON Fastcam Mini UX100 color high-speed camera. The high-speed camera 6 captures perpendicularly to the welding direction and parallel to the welding wire 9, and the fixed frame rate during shooting is 4000 frames / s.

[0066] The computer 8 is used to receive and process the image data captured by the high-speed camera 6 .

[0067] The high-speed images obtained from the experiment are as follows: Figure 2 As shown, in a selected transition period, the metal droplet 10 separates from the welding wire 9 and flies to the molten pool. The high-speed camera 6 takes a metal droplet image every 0.25ms, and finally obtains the entire image of the metal droplet 10 flying from the welding wire 9 into the molten pool.

[0068] like Figure 3 As shown in the figure, the force analysis of the metal droplet 10 shows that the metal droplet 10 is subjected to its own gravity F when it is separated from the welding wire 9 and flies to the molten pool. G Since the metal droplet 10 is wrapped in the arc plasma 11, the metal droplet 10 will be affected by the plasma flow force F of the arc plasma downward along the axis of the welding wire 9. P Since the laser beam acts on the workpiece 3 to be welded, a keyhole 13 is generated, and then the metal vapor 12 is ejected upward, so the metal droplet 10 is subjected to the upward metal vapor pressure F when it approaches the keyhole 13 m .

[0069] After the experiment, the captured metal droplet transition images were processed and analyzed. A metal droplet transition period was selected, and the average speed within each two-frame interval was calculated according to formula (1) and formula (2). The curve of the change of the metal droplet flight speed over time during the transition period was obtained, as shown in Figure 2. Figure 4 As shown, starting from the time period of 2.00s to 2.25s, the curve of the average velocity of the molten metal droplet changing with time becomes gentle, and then the slope of the curve is almost zero. Therefore, at 2.00s to 2.25s, the hindering force of the metal vapor pressure on the molten metal droplet is equal to the promoting force of the gravity and plasma flow force on the molten metal droplet, that is, this is the point 14 where the resultant force starts to be zero.

[0070]

[0071] Among them, S i x is the flying length of the metal droplet during the interval between two adjacent frames; i-1 ,y i-1 is the coordinate of the center of mass of the metal droplet in the previous frame; x i ,y i is the coordinate of the center of mass of the metal droplet in the next frame; t is the time interval between two adjacent frames; v i is the average speed in each time period.

[0072] The protective gas used in the experiment is argon. The argon plasma density under standard atmospheric pressure is calculated according to formula (3):

[0073]

[0074] Wherein, P is the standard atmospheric pressure; R is the gas constant; M is the molar mass of the shielding gas; and T is the arc temperature.

[0075] Because the slope of the velocity curve at the time of 2s to 2.25s is zero, the flying distance d of the metal droplet is between 4.3mm and 4.9mm, d>3mm, and the arc current that decays with distance has approached a constant value, so the arc current value here is calculated according to formula (4):

[0076] I=I0e -zd =260A×e -0.2883×3 =109A(4);

[0077] Among them, I0 is the arc current when the metal droplet just separates; z is a constant; d is the flight distance of the metal droplet.

[0078] In this embodiment, the proportionality coefficient between the plasma flow rate and the current value is k=0.75, so the arc plasma flow rate is calculated according to formula (5):

[0079] v f =kI=0.75×109A=81.75m / s(5);

[0080] Where k is a constant and I is the plasma current at the location of the metal droplet.

[0081] The long axis and short axis of the metal droplet during this period are measured by a high-speed camera, and the average diameter of the metal droplet is calculated according to formula (6):

[0082]

[0083] Among them, h and w are the major axis and minor axis of the metal droplet, respectively.

[0084] The arc plasma Reynolds number here is calculated according to formula (7):

[0085]

[0086] Wherein, μ is the viscosity coefficient of the high temperature protective gas.

[0087] The plasma flow coefficient here is calculated according to formula (8):

[0088]

[0089] According to formula (9), the plasma flow force on the metal droplet when the resultant force is zero is calculated:

[0090]

[0091] The gravity on the metal droplet is calculated according to formula (10):

[0092] F G =ρ d Vg=7000kg / m 3 ×0.15mm 3 ×9.8m / s 2 =1.03×10 -5 N (10).

[0093] Among them, F G is the gravity on the metal droplet; ρ d is the density of the molten metal droplet; g is the acceleration due to gravity; V is the average volume of the molten metal droplet.

[0094] Visible F G <<F P Therefore, the acceleration of the metal droplet by gravity is ignored, and only the plasma flow force is considered. Through high-speed camera image measurement, when the resultant force on the metal droplet is zero, the distance from the keyhole is about 2.96 to 3.60 mm. The metal vapor recoil pressure on the metal droplet here is about F m =F P =0.231×10 -3 N.

[0095] It is worth noting that the contents not elaborated in detail in the present invention are all prior art and are well known to those skilled in the art.

[0096] Therefore, the present invention adopts the above-mentioned estimation method and device for the impact behavior of steam eruption in a laser keyhole, which is suitable for studying the characteristic behavior of metal vapor erupting in a laser keyhole in the fields of laser welding, laser-arc hybrid welding, etc.

[0097] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for estimating the impact behavior of laser-induced steam eruption in a keyhole, characterized in that: The following steps are involved: Step S1, adding a metal droplet above the laser keyhole by means of MIG or TIG arc, obtaining the coordinates of the center of mass of the metal droplet in each frame within a flight cycle by using a high-speed camera, calculating the average speed of each time period, and obtaining a curve of the change of the flight speed of the metal droplet over time. When the slope of the change curve is zero, the position and time at which the resultant force on the metal droplet is zero are obtained; Step S2, using a high-speed camera to obtain the morphological parameters of the metal droplet in a flight cycle, and calculating the plasma flow force and gravity on the metal droplet at a point where the resultant force on the metal droplet is zero according to the relationship between the current and the flight distance of the metal droplet; Step S3, according to the static equilibrium theory, the deceleration force on the metal droplet at the point where the resultant force is zero is calculated, that is, the impact pressure exerted on the metal droplet by the steam ejected in the keyhole caused by the laser at this point.

2. The method for estimating the impact behavior of laser-induced steam eruption in a keyhole according to claim 1, characterized in that: In step S1, the average speed of each time period is calculated as follows: Among them, S i x is the length of the metal droplet flying during the interval between two adjacent frames; i-1 ,y i-1 is the coordinate of the center of mass of the metal droplet in the previous frame; x i ,y i is the coordinate of the center of mass of the metal droplet in the next frame; t is the time interval between two adjacent frames; v i is the average speed in each time period.

3. The method for estimating the impact behavior of laser-induced steam eruption in a keyhole according to claim 2, characterized in that: In step S2, the plasma flow force on the metal droplet is calculated as follows: Among them, F P is the plasma flow force on the metal droplet; C d is the plasma flow coefficient; A is the cross-sectional area of ​​the metal droplet along the axis of the welding wire; ρ f is the plasma density; v f is the plasma flow rate; ρ f The calculation formula is as follows: Wherein, P is standard atmospheric pressure; R is gas constant; M is molar mass of shielding gas; T is arc temperature; v f The calculation formula is as follows: in f =kI(5); Where k is a constant; I is the plasma current at the location of the metal droplet, and the calculation formula of I is as follows: I=I0e -zd (6); Where I0 is the arc current when the metal droplet just separates; z is a constant; d is the flying distance of the metal droplet; C d The calculation formula is as follows: Where Re is the plasma Reynolds number, and the calculation formula of Re is as follows: Wherein, μ is the viscosity coefficient of the high temperature protective gas; D is the average diameter of the metal droplet, and the calculation formula of D is as follows: Among them, h and w are the major axis and minor axis of the metal droplet, respectively.

4. The method for estimating the impact behavior of laser-induced steam eruption in a keyhole according to claim 3, characterized in that: In step S2, the gravity exerted on the metal droplet is calculated as follows: F G =ρ d Vg(10); Among them, F G is the gravity on the metal droplet; ρ d is the density of the metal droplet; g is the acceleration of gravity; V is the average volume of the metal droplet, and the calculation formula of V is as follows:

5. The method for estimating the impact behavior of laser-induced steam eruption in a keyhole according to claim 4, characterized in that: In step S3, the deceleration force on the metal droplet at the point where the resultant force is zero is calculated as follows: F m =F G +F P (12); Among them, F m For deceleration force.

6. A device for implementing the method for estimating the impact behavior of laser-induced steam eruption in a keyhole as claimed in any one of claims 1 to 5, characterized in that: It includes a workpiece to be welded, a high-power laser is arranged on the upper side of the workpiece to be welded, the high-power laser emits a laser beam perpendicular to the workpiece to be welded, a welding gun is arranged on one side of the intersection of the laser beam and the workpiece to be welded, semiconductor lighting lasers and high-speed cameras are symmetrically placed on both sides of the laser beam, the semiconductor lighting laser is connected to the semiconductor lighting laser power supply, and the high-speed camera is connected to a computer.

7. The device for estimating the impact behavior of laser-induced steam eruption in a keyhole according to claim 6, characterized in that: The high power laser is any one of a fiber laser, a Nd:YAG laser, a CO2 laser, a blue laser, a green laser or a semiconductor laser, and the laser output power is 0.5 to 50 kW.

8. The device for estimating the impact behavior of laser-induced steam eruption in a keyhole according to claim 6, characterized in that: The angle between the laser beam emitted by the high-power laser and the welding wire is 0 to 80 degrees; the distance between the laser focus point and the tip of the welding wire is -2 to 5 mm.

9. The device for estimating the impact behavior of laser-induced steam eruption in a keyhole according to claim 6, characterized in that: The shooting frame rate of the high-speed camera is 1000-50000 frames / s, and a narrow-band filter whose central band is consistent with the wavelength of the illumination light of the semiconductor illumination laser is arranged in front of the lens of the high-speed camera.

10. The device for estimating the impact behavior of laser-induced steam eruption in a keyhole according to claim 6, characterized in that: The wavelength of the illumination light of the semiconductor illumination laser is 400 to 900 nm, and the laser output power is 0.01 to 50 W.

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