A cladding layer cross-section morphology calculation method based on ultrasonic vibration assistance

Abstract

The application discloses a kind of based on ultrasonic vibration auxiliary cladding layer section appearance calculation method, laser cladding is carried out;The processing area of laser cladding is discretized and handled, and each discrete unit is regarded as a cell;Powder beam flow model is constructed;When laser cladding under the ultrasonic vibration auxiliary exists physical process, heat source model is constructed;According to powder beam flow model and heat source model, the state of each cell is obtained, and cell state includes phase state and temperature;Based on cellular automaton, the temperature transfer rule of cladding layer under the ultrasonic vibration auxiliary and the cell state of instant time are used to calculate the cell state of next time, realize cell state update;Based on ultrasonic vibration auxiliary, droplet forming method is improved, cladding layer cell distribution is calculated, and the section appearance of cladding layer is obtained.Through combining cellular automaton method and droplet forming theory under the action of vibration, more perfect cladding layer section profile calculation model is established, and the accurate calculation of cladding layer section appearance is realized.

Description

Technical Field

[0001] This invention relates to laser cladding, specifically to a method for calculating the cross-sectional morphology of the cladding layer based on ultrasonic vibration assistance. Background Technology

[0002] Laser cladding technology is increasingly used in component processing. However, the rapid temperature changes in the molten pool during cladding can lead to poor cladding layer quality. 35CrMo steel has a carbon equivalent (Ceq) of 0.72%, poor weldability, and a high tendency to harden during laser cladding, resulting in a greater susceptibility to both hot and cold cracking in the heat-affected zone (HAZ). When laser cladding is performed on a 35CrMo substrate, the HAZ of the cladding layer exhibits high microhardness, but it is also prone to cracking. Without ultrasonic vibration, the HAZ produces more cracks, including not only large main cracks but also numerous small microcracks. Research into ultrasonic vibration-assisted laser cladding technology can improve the quality of the cladding layer and promote the expansion of its applications.

[0003] Ultrasonic vibration generates acoustic flow and cavity effects during laser cladding, influencing the crystallization of molten metal by altering low gloss and nucleation rate during solidification. Ultrasonic waves demonstrate significant technological advantages in improving metal solidification structure and reducing internal porosity. Currently, some studies are gradually exploring the effects of ultrasonic vibration power or frequency on laser cladding, but the number of vibration parameters involved is relatively small. Further exploration is needed to understand the impact of more vibration parameters on the quality and morphology of the cladding layer. Furthermore, the vibration characteristics of the substrate material are uncertain, and ultrasonic energy cannot be fully transferred to the molten pool of the cladding layer. Most research is limited to microstructure and mechanical properties. There is a lack of research on the impact of ultrasonic vibration on the macroscopic morphology of the cladding layer, which will limit the processing accuracy of ultrasonic vibration-assisted laser cladding technology. In addition, current research on ultrasonic vibration-assisted laser cladding technology is mainly experimental, with a serious lack of numerical simulation studies. The establishment of computational models is an effective driving force for the development of ultrasonic vibration-assisted laser cladding technology. Summary of the Invention

[0004] Purpose of the invention: To address the above-mentioned shortcomings, this invention provides an accurate method for calculating the cross-sectional morphology of the cladding layer based on ultrasonic vibration assistance.

[0005] Technical solution: To solve the above problems, this invention employs a method for calculating the cross-sectional morphology of the cladding layer based on ultrasonic vibration assistance, comprising the following steps:

[0006] (1) Apply ultrasonic vibration to the substrate;

[0007] (2) The four-channel coaxial powder feeding nozzle sprays the laser beam and powder beam onto the substrate surface to form a cladding layer and perform laser cladding; the processing area of ​​laser cladding is discretized, and each discrete unit is a cell;

[0008] (3) Construct a powder beam model to describe the concentration distribution of the four powder beams under the four-channel powder feeding nozzle;

[0009] (4) Construct a heat source model based on the physical processes involved in laser cladding under ultrasonic vibration assistance;

[0010] (5) The state of each cell is obtained based on the powder beam model and the heat source model. The cell state includes the phase state and temperature.

[0011] (6) Based on the cellular automata, the cell state at the next moment is calculated according to the temperature transfer rules of the cladding layer under ultrasonic vibration assistance and the instantaneous cell state, so as to realize the cell state update;

[0012] (7) Based on the improved droplet forming method of ultrasonic vibration, the distribution of cladding cell is calculated according to the spreading process of liquid cell, and the cross-sectional morphology of cladding layer is obtained.

[0013] Furthermore, the substrate is made of 35CrMo material. In step (1), the natural frequency of the 35CrMo substrate material is first determined, or the 35CrMo substrate material is designed into a specific shape to have a specific natural frequency, which is 15kHz or 20kHz.

[0014] Furthermore, in step (3), the centers of the four powder beams under the four-channel powder feeding nozzle do not coincide, and the expression for the powder beam concentration distribution is:

[0015]

[0016] in, , , , The concentration distributions of the four powder beams are shown below. This refers to the powder mass concentration on a horizontal substrate. The amount of powder entering each unit length of the molten pool; F is the powder feed rate, S is the scanning speed, and H is the vertical distance between the four-channel coaxial powder feed nozzle and the horizontal substrate surface. It is half the powder beam divergence angle. It is the angle between the coaxial powder feeder shaft and the horizontal base.

[0017] Furthermore, the laser acts as a heat source to provide heat input to the powder, and the laser heat source power density... The expression is:

[0018]

[0019] in, For laser power, The attenuation rate of the powder to the laser energy is denoted as . and These represent the positions of the current cell in the cellular space. The laser spot radius is... The velocity of the laser along the X-axis. Let t be the velocity of the laser along the Y-axis, and t be the laser travel time. The unit cell size.

[0020] The applied ultrasonic vibration generates a thermal effect on the cladding layer and the substrate, and the power density of the ultrasonic vibration... The expression is:

[0021]

[0022] in, is the constant of the ultrasonic absorption coefficient. The speed at which ultrasound propagates. The vibration frequency, Density of powder material The amplitude is denoted as .

[0023] During ultrasonic vibration-assisted laser cladding, in addition to absorbing energy from the laser and ultrasonic vibrations, the cladding layer also experiences energy loss due to radiation and convection between the cladding layer and the air. Therefore, the temperature rise of the cladding layer powder is:

[0024]

[0025] in, The position is The temperature change value of the cell. It is the laser power density. It is the power density of energy lost through convective heat dissipation. It is the power density of energy lost through radiation and heat dissipation. For specific heat capacity, The density is the powder material density.

[0026] Furthermore, in step (7), the droplet forming method describes the total energy of the molten droplet. The expression is:

[0027]

[0028] in, Represents the surface free energy of the solid-gas interface. Represents the surface free energy of the solid-liquid interface. Represents the surface free energy of the liquid-gas interface; This represents the boundary area of ​​each cell at the liquid-gas interface. This represents the boundary area of ​​each cell at the solid-liquid interface. It is the density of the liquid. It is the gravitational acceleration constant. It is the volume of the liquid cell. It is the height of the center of mass of the liquid cell. When When the minimum value is reached, the final distribution of the cladding layer cells is obtained, and the cross-sectional morphology of the cladding layer is obtained based on the distribution of the cladding layer cells.

[0029] The steps for analyzing the quality of the cladding layer in this invention are as follows:

[0030] The cross-section of a single-pass cladding layer was cut using wire electrical discharge machining (EDM). The cross-sectional morphology of the cladding layer was observed using a stereomicroscope. Three cross-sections were cut from each track, and their dimensional parameters were measured and averaged. The contact angle and cross-sectional area were calculated after fitting a spline curve to the cross-sectional morphology of the cladding layer.

[0031] After laser cladding, the samples were cut, ground, polished, and etched, and then their microstructure was observed and analyzed using metallographic techniques. The polished samples were then subjected to microhardness testing of the cladding layer using a digital microhardness tester.

[0032] Beneficial effects: Compared with the prior art, the significant advantage of this invention is that by combining the cellular automata method and droplet forming theory, a more complete calculation model of the cross-sectional profile of the cladding layer is established with the assistance of ultrasonic vibration. During laser cladding, the resonance between the substrate material and the ultrasonic vibration device allows the energy of the ultrasonic vibration to be more fully transferred to the molten pool of the cladding layer, and the law of ultrasonic vibration is easier to control, thus achieving accurate calculation of the cross-sectional morphology of the cladding layer. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the calculation process for the cladding cross-sectional morphology of the present invention;

[0034] Figure 2 This is a schematic diagram of the device structure for laser cladding according to the present invention;

[0035] Figure 3 This is a cross-sectional view of the 35CrMo special substrate used in this invention;

[0036] Figure 4 (a) is a cross-sectional morphology diagram of the cladding layer in the present invention when there is no vibration power. Figure 4 (b) is a cross-sectional morphology diagram of the cladding layer when the vibration power is 260W in this invention. Figure 4 (c) is a cross-sectional morphology diagram of the cladding layer when the vibration power is 520W in this invention. Figure 4(d) in the figure is a cross-sectional morphology diagram of the cladding layer when the vibration power is 780W in this invention;

[0037] Figure 5 This describes the microstructure of the cladding layer under different vibration powers in this invention.

[0038] Figure 6 This refers to the microhardness of the cladding layer under different vibration powers in this invention;

[0039] Figure 7 This describes the crack distribution in the heat-affected zone of the cladding layer under different vibration powers in this invention. Detailed Implementation

[0040] like Figure 1 As shown in this embodiment, a method for calculating the cross-sectional morphology of a laser cladding layer includes the following steps:

[0041] (1) Apply ultrasonic vibration at the resonant frequency to substrate 1; substrate 1 is made of 35CrMo material. First, the natural frequency of the 35CrMo substrate material is measured, or the 35CrMo substrate material is designed into a specific shape to have a specific natural frequency, which is 15kHz or 20kHz.

[0042] To ensure the resonance of substrate 1, the modal frequencies and mode shapes of the substrate were calculated using the finite element method. A finite element model of the dedicated substrate was established using Abaqus software. The substrate was meshed using three-dimensional stress elements C3D4, and the mesh was refined based on a frequency convergence criterion of less than 1%. Considering the accuracy and efficiency of finite element calculation, the Lanczos method was chosen to extract the modal characteristics of the dedicated substrate. According to the finite element analysis results, the natural frequency of the dedicated substrate is 19.737 kHz, which is close to the resonant frequency of the ultrasonic system (20 kHz).

[0043] Then, the special substrate is fastened to the ultrasonic transducer 2 with M12*1.75 bolts so that it can resonate with the transducer under the action of ultrasonic vibration.

[0044] Next, the ultrasonic vibration device 3 is fixed on the worktable of the laser cladding equipment from the vibration node of the transducer.

[0045] (2) Laser cladding equipment is used to clad the vibrating 35CrMo substrate. The four-channel coaxial powder feeding nozzle sprays the laser beam 5 and the powder beam 6 onto the substrate surface to form the cladding layer 4 and perform laser cladding. The processing area of ​​laser cladding is discretized, and each discrete unit is a cell.

[0046] (3) Construct a powder beam model, which describes the concentration distribution of the four powder beams under the four-channel powder feeding nozzle; the centers of the four powder beams under the four-channel powder feeding nozzle do not coincide, and the expression for the concentration distribution of the powder beam is:

[0047]

[0048] in, , , , The concentration distributions of the four powder beams are shown below. This refers to the powder mass concentration on a horizontal substrate. The amount of powder entering each unit length of the molten pool is defined as follows: F is the powder feeding rate (1.0 r / min in this embodiment), V is the scanning speed (300 mm / min); H is the vertical distance between the four-channel coaxial powder feeding nozzle and the horizontal substrate surface. It is half the powder beam divergence angle. It is the angle between the coaxial powder feeder shaft and the horizontal base.

[0049] (4) Construct a heat source model based on the physical processes involved in laser cladding with ultrasonic vibration assistance; the physical processes include: the shielding effect of the alloy powder material on the laser energy; the heat input of the laser and ultrasonic vibration applied to the alloy powder and the substrate surface; and the energy loss caused by radiation and convection between the cladding layer and the air.

[0050] When the powder material blocks the laser energy, the laser acts as a heat source, providing heat input to the powder. The laser heat source power density... The expression is:

[0051]

[0052] in, For laser power, The attenuation rate of the powder to the laser energy is denoted as . and These represent the positions of the current cell in the cellular space. The laser spot radius is... The velocity of the laser along the X-axis. Let t be the velocity of the laser along the Y-axis, and t be the laser travel time. The unit cell size.

[0053] The applied ultrasonic vibration generates a thermal effect on the cladding layer and the substrate, and the power density of the ultrasonic vibration... The expression is:

[0054]

[0055] in, is the constant of the ultrasonic absorption coefficient. The speed at which ultrasound propagates. The vibration frequency, Density of powder material The amplitude is denoted as .

[0056] During ultrasonic vibration-assisted laser cladding, in addition to absorbing energy from the laser and ultrasonic vibrations, the cladding layer also experiences energy loss due to radiation and convection between the cladding layer and the air. Therefore, the temperature rise of the cladding layer powder is:

[0057]

[0058] in, The position is The temperature change value of the cell. It is the laser power density. It is the power density of energy lost through convective heat dissipation. It is the power density of energy lost through radiation and heat dissipation. For specific heat capacity, The density is the powder material density.

[0059] (5) Set the material phase transition rules for the laser cladding process: When the temperature of the metal material exceeds its melting point, it will melt; conversely, when the temperature of the metal material drops to the corresponding temperature range, it will solidify. The state of each cell is obtained according to the powder beam model and the heat source model. Each cell is set with two states: phase state S and temperature state T. The S state indicates that the current cell is a liquid cell, solid cell, boundary cell or gas cell, and the T state indicates the temperature of the current cell.

[0060] (6) Based on the cellular automata, the cell state at the next moment is calculated according to the temperature transfer rules of the cladding layer under ultrasonic vibration assistance and the instantaneous cell state, so as to realize the cell state update; the temperature transfer rules of the cladding layer are: the heat input of the laser loaded on the alloy powder and the substrate surface; the heat conduction inside the solid material; the heat convection and heat conduction of the molten liquid in the molten pool; the convective heat transfer and radiative heat transfer between the substrate and the cladding layer surface and the air.

[0061] (7) Using the droplet forming method, the distribution of cladding cells is calculated based on the spreading process of liquid cells under ultrasonic vibration assistance, and the cross-sectional morphology of the cladding layer is obtained.

[0062] Droplet formation methods describe the total energy of molten droplets. The expression is:

[0063]

[0064] in, Represents the surface free energy of the solid-gas interface. Represents the surface free energy of the solid-liquid interface. Represents the surface free energy of the liquid-gas interface; This represents the boundary area of ​​each cell at the liquid-gas interface. This represents the boundary area of ​​each cell at the solid-liquid interface. It is the density of the liquid. It is the gravitational acceleration constant. It is the volume of the liquid cell. It is the height of the center of mass of the liquid cell. When When the minimum value is reached, the final distribution of the cladding layer cells is obtained, and the cross-sectional morphology of the cladding layer is obtained based on the distribution of the cladding layer cells.

[0065] like Figures 3 to 6 As shown, the cross-section of the cladding layer was cut using electrical discharge machining (EDM) to analyze the effect of ultrasonic vibration on the cladding quality. The cross-sectional morphology of the cladding layer was observed using a stereomicroscope. The dimensional parameters of three cross-sections were cut from each track and measured, and the average value was taken. The contact angle and cross-sectional area were calculated after fitting a spline curve to the cross-sectional morphology of the cladding layer.

[0066] After laser cladding, the samples were cut, ground, polished, and etched, and then their microstructure was observed and analyzed using metallographic techniques. The polished samples were then subjected to microhardness testing of the cladding layer using a digital microhardness tester.

[0067] The processing parameters for laser cladding are set as follows: laser power P=1300W, powder feeding rate F=1.0r / min, and scanning speed V=300mm / min.

[0068] The ultrasonic generator signal frequency was set to the natural frequency of the substrate material, 20kHz, and the vibration power was set to 260W. The microhardness test results of the cladding layer are shown in Table 1.

[0069] Table 1

[0070] <![CDATA[Average microhardness HV of the heat affected zone 0.2 > 542.6 917.5

[0071] The ultrasonic generator signal frequency was set to the natural frequency of the substrate material, 20kHz, and the vibration power was set to 520W. The microhardness test results of the cladding layer are shown in Table 2.

[0072] Table 2

[0073] <![CDATA[Average microhardness HV of the heat affected zone 0.2 > 542.6 758.3

[0074] The ultrasonic generator signal frequency was set to the natural frequency of the substrate material, 20kHz, and the vibration power was set to 780W. The microhardness test results of the cladding layer are shown in Table 3.

[0075] Table 3

[0076] <![CDATA[Average microhardness HV of the heat affected zone 0.2 > 542.6 795

Claims

1. A method for calculating the cross-sectional morphology of cladding layer based on ultrasonic vibration assistance. Its features are, Includes the following steps: (1) Apply ultrasonic vibration to the substrate; (2) The four-channel coaxial powder feeding nozzle sprays the laser beam and powder beam onto the substrate surface to form a cladding layer and perform laser cladding; the processing area of ​​laser cladding is discretized, and each discrete unit is a cell; (3) Construct a powder beam model to describe the concentration distribution of the four powder beams under the four-channel powder feeding nozzle; (4) A heat source model is constructed based on the physical processes involved in laser cladding under ultrasonic vibration assistance. The physical processes include: the shielding effect of the alloy powder material on the laser energy; the heat input of the laser and ultrasonic vibration applied to the alloy powder and the substrate surface; and the energy loss caused by radiation and convection between the cladding layer and the air. (5) The state of each cell is obtained based on the powder beam model and the heat source model. The cell state includes the phase state and temperature. (6) Based on the cellular automata, the cell state at the next moment is calculated according to the temperature transfer rules of the cladding layer under ultrasonic vibration assistance and the instantaneous cell state, so as to realize the cell state update; (7) Using the droplet forming method, the distribution of cladding cells is calculated based on the spreading process of liquid cells under ultrasonic vibration assistance, and the cross-sectional morphology of the cladding layer is obtained.

2. The method for calculating the cross-sectional morphology of the cladding layer according to claim 1, characterized in that, The substrate is made of 35CrMo material. In step (1), the natural frequency of the 35CrMo substrate material is first measured, or the 35CrMo substrate material is designed into a specific shape to have a specific natural frequency, which is 15kHz or 20kHz.

3. The method for calculating the cross-sectional morphology of the cladding layer according to claim 1, characterized in that, In step (3), the centers of the four powder beams under the four-channel powder feeding nozzle do not coincide, and the expression for the powder beam concentration distribution is: in, , , , The concentration distributions of the four powder beams are shown below. This refers to the powder mass concentration on a horizontal substrate. The amount of powder entering each unit length of the molten pool; F is the powder feed rate, S is the scanning speed, and H is the vertical distance between the four-channel coaxial powder feed nozzle and the horizontal substrate surface. It is half the powder beam divergence angle. It is the angle between the coaxial powder feeder shaft and the horizontal base.

4. The method for calculating the cross-sectional morphology of the cladding layer according to claim 3, characterized in that, Laser is used as a heat source to provide heat input to powder; laser heat source power density The expression is: in, For laser power, The attenuation rate of the powder to the laser energy is denoted as . and These represent the coordinates of the current cell's position in the cellular space. The laser spot radius is... The velocity of the laser along the X-axis. Let t be the velocity of the laser along the Y-axis, and t be the laser travel time. The unit cell size.

5. The method for calculating the cross-sectional morphology of the cladding layer according to claim 4, characterized in that, The applied ultrasonic vibration generates a thermal effect on the cladding layer, and the power density of the ultrasonic vibration... The expression is: in, is the constant of the ultrasonic absorption coefficient. The speed at which ultrasound propagates. The vibration frequency, Density of powder material The amplitude is denoted as .

6. The method for calculating the cross-sectional morphology of the cladding layer according to claim 5, characterized in that, During ultrasonic vibration-assisted laser cladding, in addition to absorbing energy from the laser and ultrasonic vibrations, the cladding layer also experiences energy loss due to radiation and convection between the cladding layer and the air. Therefore, the temperature rise of the cladding layer powder is: in, The position is The temperature change value of the cell. It is the laser power density. It is the power density of energy lost through convective heat dissipation. It is the power density of energy lost through radiation and heat dissipation. For specific heat capacity, The density is the powder material density.

7. The method for calculating the cross-sectional morphology of the cladding layer according to claim 1, characterized in that, In step (7), the droplet forming method describes the total energy of the molten droplet. The expression is: in, Represents the surface free energy of the solid-gas interface. Represents the surface free energy of the solid-liquid interface. Represents the surface free energy of the liquid-gas interface; This represents the boundary area of ​​each cell at the liquid-gas interface. This represents the boundary area of ​​each cell at the solid-liquid interface. It is the density of the liquid. It is the gravitational acceleration constant. It is the volume of the liquid cell. It is the height of the center of mass of the liquid cell.

8. The method for calculating the cross-sectional morphology of the cladding layer according to claim 7, characterized in that, when When the minimum value is reached, the final distribution of the cladding layer cells is obtained, and the cross-sectional morphology of the cladding layer is obtained based on the distribution of the cladding layer cells.

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