A welding head suitable for ultrasonic continuous welding and its design method

Abstract

The present invention provides a welding head suitable for ultrasonic continuous welding and a design method thereof, belonging to the technical field of thermoplastic composite material welding, comprising a welding head body, the welding head body comprising an input section, a transition curved surface section and an output section, the input section and the output section of the welding head body being stepped, the transition curved surface section being in the shape of a "~", and the cross section of the welding head body in the length direction being rectangular. The present invention constructs a piecewise function of the cross-sectional area in the length direction of the welding head body through the dimensional parameters of the input section and the output section and the cubic polynomial curve of the transition curved surface section, thereby obtaining the welding head body. The transition curve of the present invention has a continuous curvature, a stable structure, and uniform force. It still has a high deformation resistance under the combined action of longitudinal alternating loads and transverse friction forces, and can effectively reduce the heat concentration phenomenon in the welding area, thereby improving the uniformity of the weld seam of continuous welding; at the same time, since the rectangular cross-section welding head has uniform stress distribution during the welding process, it can effectively improve the joint strength.

Description

Technical Field

[0001] The invention belongs to the technical field of thermoplastic composite material welding, and in particular relates to a welding head suitable for ultrasonic continuous welding and a design method thereof. Background Art

[0002] Thermoplastic composites, due to their low density, superior mechanical properties, low processing costs, and recyclability, have been widely used in industries such as automotive, aerospace, and medical devices that pursue lightweight, high-performance components. However, the high viscosity of thermoplastic composite matrices limits their processability, necessitating more efficient joining technologies. Ultrasonic welding is a commonly used joining technology for composite materials, offering advantages such as fast welding speed, high weld strength, excellent sealing, clean and pollution-free operation, and low cost.

[0003] With the widespread application of thermoplastic composites in large composite structural parts such as carbon fiber car bodies, carbon fiber automobile chassis, carbon fiber trailers, and aircraft fuselage midsections, traditional ultrasonic single-point static welding technology is difficult to achieve the connection of large-size joints in the above-mentioned structural parts due to the limitation of welding head size.

[0004] To solve the above problems, researchers in related fields have further carried out research on ultrasonic continuous welding. Ultrasonic continuous welding refers to the continuous relative movement of the weldment and the welding head along the welding plane during ultrasonic welding to form a continuous and complete weld.

[0005] Compared with the traditional ultrasonic single-point static welding process, the ultrasonic continuous welding process requires the welding head to bear the additional friction force F generated by the relative movement with the weld surface. f , F f Opposite to the moving direction of the welding head and perpendicular to the vibration direction of the welding head, F f The presence of this leads to uneven vibration distribution on both sides of the ultrasonic wave transmission direction of the welding head during ultrasonic continuous welding, causing lateral vibration of the welding head, seriously affecting the welding quality and welding head life, and even damaging the welding machine. In addition, the heat generation area of ​​ultrasonic welding is related to the shape of the welding head end. Traditional circular cross-section welding heads are prone to stress concentration during the welding process. At the beginning of welding, the heat generation efficiency in the center of the welding area is high and decays to the surrounding area. As the welding head continues to stay, the heat generation area spreads from the center to the surrounding area. However, the welding head of ultrasonic continuous welding does not stop relative to the workpiece, and traditional circular cross-section welding heads are not suitable for ultrasonic continuous welding.

[0006] Patent No. CN112743218B discloses an ultrasonic welding horn with an indenter. The horn's output section is knurled, with the knurled tip contacting the workpiece and transferring energy to it. However, the horn's output section cannot suppress uneven vibration distribution. Furthermore, the knurling on the horn's output section increases friction with the workpiece's upper surface, making it unsuitable for continuous ultrasonic welding.

[0007] Patent No. CN216466265U discloses an ultrasonic welding head that does not stick to materials. This head controls the movement of a pressing plate to press the material as it separates from the welding head. However, this welding head cannot suppress the uneven vibration distribution of the welding head and the stress concentration that is common with traditional circular cross-section welding heads during welding, making it unsuitable for continuous ultrasonic welding.

[0008] Patent No. CN216466267U discloses an ultrasonic welding head with a replaceable head. While ensuring a secure connection, this head improves head replacement efficiency and reduces damage to the head. However, this welding head cannot suppress the uneven distribution of welding head vibration and the stress concentration that is common during welding with traditional circular cross-section welding heads, making it unsuitable for continuous ultrasonic welding.

[0009] Therefore, it is very necessary to develop a welding head suitable for ultrasonic continuous welding. Summary of the Invention

[0010] In the current ultrasonic continuous welding process of thermoplastic composite materials, the friction force F f This causes uneven vibration distribution on both sides of the welding head in the direction of sound wave transmission, resulting in poor welding quality and damage to the welding head and welding machine; and the stress concentration in the welding area of ​​the traditional circular cross-section welding head makes it difficult to achieve continuous welding of large-size components. The present invention provides a welding head suitable for ultrasonic continuous welding and a design method thereof, which has a simple process, good welding effect, and can effectively improve the uneven vibration distribution during the welding process of the welding head and the stress concentration that is prone to occur in the welding process of the traditional circular cross-section welding head.

[0011] In order to solve the above technical problems, the technical solution adopted by the present invention is: a welding head suitable for ultrasonic continuous welding, including a welding head body, the welding head body including an input section, a transition curved section and an output section, the input section and the output section of the welding head body are stepped, that is, the two ends of the welding head body are stepped, and there is a transition curved section between the input section and the output section of the welding body, and the transition curved section is in the shape of "~", the cross-section of the welding head body in the length direction is rectangular, and the welding head body is an integrally formed structure.

[0012] Therefore, the cross-sectional area function of the welding head body in the length direction is:

[0013]

[0014] Where S(x) is the cross-sectional area of ​​the welding head body in the length direction, w0 is the width of the input section, w1 is the width of the output section, d is the thickness of the welding head body, l1 is the length of the input section, l2 is the length of the transition surface section, h(x) is the transition curve function on one side of the transition surface section, and l is the length of the welding head body;

[0015] The output section of the welding head body is provided with chamfered corners on both sides perpendicular to the welding direction.

[0016] The present invention also provides a method for designing a welding head suitable for ultrasonic continuous welding, comprising the following steps:

[0017] S1. Determine the size of the input section and output section of the welding head body: the width w0 of the input section of the welding head body and the thickness d of the welding head body are equal to the diameter D of the output end of the amplitude transformer, w0 = d = D; the width w1 of the output section depends on the amplitude magnification factor; when the amplitude magnification factor is N, w 1＝ w0 / N;

[0018] S2. Determine the length of the welding head body: Calculate the wavelength λ of the ultrasonic wave transmitted by the welding head body according to the material properties of the welding head body, and determine the length l of the welding head body, the length l1 of the input section, the length l2 of the transition surface section, and the length l3 of the output section;

[0019] S3. Select the transition curve nodes of the transition surface segment: Considering the size of the input and output segments of the welding head body and the stability of vibration transmission, since the welding head body is an axisymmetric structure, select n nodes (n ≥ 4) required for the "~"-shaped transition curve on one side of the transition surface segment;

[0020] S4. Calculate the transition curve expression: Use the least squares method to fit a cubic polynomial to perform curve fitting on the n nodes selected in step S3 to obtain the transition curve expression h(x) on one side of the transition surface segment;

[0021] S5. Construct a piecewise function of the cross-sectional area of ​​the welding head body in the longitudinal direction: Construct a piecewise function H(x) of the width of one side of the welding head body based on the dimensional parameters w0, w1, l, l1, l2 obtained in steps S1 and S2 and the cubic polynomial curve h(x) obtained in step S4:

[0022]

[0023] Symmetrically transform the width piecewise function H(x) along the x-axis to obtain the width piecewise function -H(x) on the symmetric side;

[0024]

[0025] Therefore, the overall width of the welding head body W(x) = 2H(x), that is,

[0026]

[0027] The area enclosed by W(x) and d is the cross-sectional area S(x) of the welding head body in the longitudinal direction, that is,

[0028]

[0029] Where x∈[0,l1) refers to the cross-section set of the input section along the length of the welding head body; x∈(l1,l1+l2) refers to the cross-section set of the transition section along the length of the welding head body; x∈

[0030] (l1+l2,l] refers to the cross-section set of the welding head body along the length direction at the output end;

[0031] S6. Forming a welding head body: superimposing the longitudinal cross-sections of the welding head body obtained in step S5 along the longitudinal direction to obtain a welding head body.

[0032] Furthermore, in step S2, l is half of the ultrasonic wavelength, l=λ / 2, and the relationship among the input section length l1, the transition surface section length l2, and the output section length l3 is: l1=l3=l2 / 2=λ / 8.

[0033] Furthermore, in step S3, a rectangular coordinate system is established with the geometric center of the cross section of the input segment end as the origin, the end node coordinates are determined by the length of the transition surface segment, the node abscissa is determined by the length of the welding head body; the node ordinate is determined by the width of the welding head input segment and output segment.

[0034] Furthermore, it is determined whether the welding head body obtained in step S6 meets the frequency tracking range of the ultrasonic generator: a model of the obtained welding head body is established for modal analysis to solve the natural frequency of the longitudinal vibration mode of the welding head body. If the natural frequency is within the frequency tracking range of the ultrasonic generator, no structural optimization is required; if the natural frequency is not within the frequency tracking range of the ultrasonic generator, structural optimization is required.

[0035] Furthermore, the method for optimizing the structure of the welding head body is to adjust the sizes of l1 and l3 to perform shape optimization based on the natural frequency.

[0036] Furthermore, modal analysis is performed on the optimized welding head model to solve the natural frequency of the longitudinal vibration mode of the welding head and verify the optimization results.

[0037] Due to the adoption of the above technical solution, the present invention has the following beneficial effects:

[0038] The "~"-shaped transition curve of the present invention has a continuous curvature, a stable structure, and a uniform force. It still has a high anti-deformation ability under the combined action of the longitudinal alternating load and the transverse friction force, and can effectively improve the friction force F between the welding head and the upper surface of the weldment. f This causes uneven vibration distribution of the welding head on both sides of the sound wave transmission direction, resulting in poor welding quality and damage to the welding head and welding machine.

[0039] The cross-section of the welding head of the present invention in the length direction is rectangular, and the heat distribution is more uniform than that of the traditional circular cross-section welding head, which can effectively reduce the heat concentration phenomenon in the welding area and improve the uniformity of the weld of continuous welding; at the same time, since the rectangular cross-section welding head has uniform stress distribution during the welding process, the fibers at the joint of the composite material weldment are evenly mixed, effectively improving the joint strength.

[0040] The weld head output end of the present invention has rounded corners on both sides perpendicular to the welding direction, which helps to reduce friction between the weld head and the weldment and reduces the impact on the weldment surface.

[0041] The welding head structure of the present invention is easy to optimize. When the natural frequency is not within the frequency tracking range of the ultrasonic generator, it is only necessary to adjust the lengths l1 and l3. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The present invention will be described in detail below with reference to the accompanying drawings and in combination with examples, and the advantages and implementation modes of the present invention will become more apparent. The contents shown in the accompanying drawings are only used to illustrate the present invention and do not constitute any limitation to the present invention. In the accompanying drawings:

[0043] Figure 1 Schematic diagram of parameters of the welding head body of the present invention.

[0044] Figure 2 It is a cubic polynomial curve on one side of the transition curved surface section of the welding head body of the present invention.

[0045] Figure 3 It is the overall width cross section of the welding head body of the present invention.

[0046] Figure 4 Schematic diagram of the welding head of Example 1 of the present invention.

[0047] Figure 5 Schematic diagram of the welding head according to embodiment 2 of the present invention.

[0048] In the picture:

[0049] 1. Input segment; 2. Transition surface segment; 3. Output segment. DETAILED DESCRIPTION

[0050] The present invention is further described below in conjunction with examples and accompanying drawings:

[0051] like Figures 1 to 5As shown, the present invention is a welding head suitable for ultrasonic continuous welding, including a welding head body, which is in a stepped "~" shape. The welding head body combines the characteristics of a stepped welding head and a "~"-shaped welding head. The welding head body includes an input section 1, a transition curved surface section 2 and an output section 3. The input section 1 and the output section 3 of the welding head body are stepped, that is, the two ends of the welding head body are stepped, and the transition curved surface section 2 is between the input section 1 and the output section 3 of the welding body. The transition curved surface section 2 is in a "~" shape. The cross-section of the welding head body is rectangular, and the two sides of the output section 3 of the welding head body perpendicular to the welding direction are set to be chamfered.

[0052] The cross-sectional area function of the welding head body is:

[0053]

[0054] Where S(x) is the cross-sectional area of ​​the welding head body in the length direction, w0 is the input section width, w1 is the output section width, d is the welding head body thickness, l1 is the input section length, l2 is the transition surface section length, h(x) is the transition curve function on one side of the transition surface section, and l is the welding head body length.

[0055] Example 1:

[0056] The welding head designed in this embodiment is made of 7075 aluminum alloy, the rated power of the ultrasonic welding machine is 2600W (high power working condition), the operating frequency f is 20KHz, the frequency tracking range of the ultrasonic generator is ±400Hz, the output end diameter of the amplitude transformer D = 30mm, the amplitude amplification factor is 2, and the transition curved surface segment is a "~" shaped surface.

[0057] like Figure 1 As shown, the present embodiment provides a method for designing a welding head suitable for ultrasonic continuous welding, comprising the following steps:

[0058] S1. Determine the dimensions of the input and output sections of the welding head body: The cross-section of the welding head body in the longitudinal direction is rectangular. The width w0 of the input section and the thickness d of the welding head body are both equal to the diameter D of the output end of the horn. The width w1 of the output section depends on the amplitude magnification factor. When the amplitude magnification factor is N, w1 = w0 / N.

[0059] That is, w0=d=30mm; w1=w0 / 2=15mm.

[0060] S2. Determine the length of the welding head body: Calculate the wavelength of the ultrasonic wave transmitted by the welding head based on its material properties, and determine the length l of the welding head body, the length l1 of the input section, the length l2 of the transition surface section, and the length l3 of the output section. Where l is half of the ultrasonic wave length, i.e. l ​​= λ / 2. The relationship between the length l1 of the input section, the length l2 of the transition surface section, and the length l3 of the output section is: l1 = l3 = l2 / 2 = λ / 8.

[0061] The Young's modulus of 7075 aluminum alloy is E = 72GPa, and the density is ρ = 2810kg / m 3 , the ultrasonic sound speed c can be solved by the following formula:

[0062]

[0063] The calculated value c = 5061.9 m / s, and the ultrasonic wavelength λ can be solved by the following formula:

[0064]

[0065] It is calculated that λ=0.253m, the welding head length l is half of the ultrasonic wavelength, that is, l=126.5mm, and the relationship between the input section length l1, the transition surface section length l2, and the output section length l3 is: l1=l3=l2 / 2=λ / 8, that is, l1=l3=31.625mm, l2=63.25mm.

[0066] S3. Select the transition curve nodes of the transition surface segment: Considering the size of the input and output segments of the welding head and the stability of vibration transmission, since the welding head body is an axisymmetric structure, select n nodes (n ≥ 4) required for the "~"-shaped transition curve on one side of the transition surface segment;

[0067] like Figure 2 As shown, in step S3, a rectangular coordinate system is established with the geometric center of the cross section at the end of the welding head input section as the origin, the end node abscissa is determined by the length of the transition surface section, and the node ordinate is determined by the width of the welding head input section and output section.

[0068] When w0 = 30 mm, w1 = 15 mm, l1 = l3 = 31.625 mm, and l2 = 63.25 mm, nodes A (31.625, 15) and E (94.875, 7.5) are determined from the transition surface segment, and the midpoint of segment AE is selected as node C (63.25, 11.25). To ensure stable energy transmission and uniform vibration distribution during welding, all nodes are equally spaced and symmetrical around the center of node C. Therefore, nodes B (47.4375, 14) and D (79.0625, 8.5) are selected.

[0069] S4. Calculate the transition curve expression: Use the least squares method to fit a cubic polynomial to perform curve fitting on the five nodes selected in step S3 to obtain the transition curve expression h(x) on one side of the transition surface segment;

[0070] The key to generating the "~"-shaped transition surface segment in this embodiment is to design and calculate the corresponding transition curve (see Figure 2 ), so this embodiment performs detailed calculations to obtain the curve equation h(x). In this embodiment, the five nodes taken are:

[0071] A: x0=31.625, h(x0)=15; B: x1=47.4375, h(x1)=14; C: x2=63.25,

[0072] h(x2)=11.25; D: x3=79.0625, h(x3)=8.5; E: x4=94.875, h(x4)=7.5;

[0073] Assume that the fitting cubic polynomial is h(x)=a0+a1x+a2x 2 +a3x 3 , the canonical equations are:

[0074]

[0075] When n=5, we can calculate:

[0076]

[0077]

[0078]

[0079] Substituting the above results into the canonical equations, we get:

[0080]

[0081] The solution is:

[0082] a0=4.75, a1=0.693, a2=-0.014, a3=0.000073771,

[0083] The cubic polynomial curve expression can be obtained:

[0084] h(x)=4.75+0.693x-0.014x 2 +0.000073771x 3 x∈(31.625,94.875).

[0085] S5. Construct a piecewise function of the cross-sectional area of ​​the welding head body in the longitudinal direction: Construct a piecewise function H(x) of the width of one side of the welding head body (in the positive direction of the coordinate axis) based on the dimensional parameters w0, w1, l, l1, and l2 obtained in steps S1 and S2 and the cubic polynomial curve h(x) obtained in step S4;

[0086]

[0087] Symmetrically transform the width piecewise function H(x) along the x-axis, and obtain the width piecewise function of the symmetric side as -H(x);

[0088]

[0089] Therefore, the overall width function of the welding head body W(x)=2H(x), that is,

[0090]

[0091] Then the area enclosed by W(x) and d is the cross-sectional function S(x) along the length direction of the welding head body, that is,

[0092]

[0093] Where x∈[0,l1) refers to the cross-section set of the input section along the length of the welding head body; x∈(l1,l1+l2) refers to the cross-section set of the transition section along the length of the welding head body; x∈

[0094] (l1+l2,l] refers to the cross-section set of the welding head body along the length direction at the output end;

[0095] In this embodiment, specifically:

[0096]

[0097]

[0098] Therefore, if Figure 3 As shown, the overall width of the welding head body W(x) = 2H(x), that is,

[0099]

[0100] Then the area enclosed by W(x) and d is the cross-sectional function S(x) along the length direction of the welding head body, that is,

[0101]

[0102] S6, forming the welding head body: superimposing the longitudinal cross-section segments of the welding head body obtained in step S5 along the longitudinal direction, such as Figure 4 As shown, the welding head body is obtained under high power working conditions.

[0103] Furthermore, it is determined whether the welding head body obtained in step S6 meets the frequency tracking range of the ultrasonic generator: a model of the obtained welding head body is established for modal analysis to solve the natural frequency of the longitudinal vibration mode of the welding head body. If the natural frequency is within the frequency tracking range of the ultrasonic generator, no structural optimization is required; if the natural frequency is not within the frequency tracking range of the ultrasonic generator, structural optimization is required.

[0104] The solution is as follows:

[0105] The general dynamic equation of the welding head is:

[0106] [M]{x″}+[C]{x′}+[K]{x}={F(t)}

[0107] Where [M] is the mass matrix; [C] is the damping matrix; [K] is the stiffness matrix; {x} is the displacement vector; {F(t)} is the force vector; {x′} is the velocity vector; {x″} is the acceleration vector, and t is time.

[0108] Undamped modal analysis is an eigenvalue problem, and the motion equations for the dynamics problem are as follows:

[0109] [M]{x″}+[K]{x}=0

[0110] The free vibration of the welding head is a simple harmonic vibration, that is, the displacement is a sine function:

[0111] x=x0 sin(ωt)

[0112] Where x0 is the displacement amplitude and ω is the angular frequency, then:

[0113] x″=-ω 2 x0 sin(ωt)=-ω 2 x

[0114] Therefore, substituting x″ into the above motion equation, we can obtain:

[0115] -ω 2 [M]{x}+[K]{x}={0}

[0116] Right now

[0117] [K]{x}=ω 2 [M]{x}

[0118] Taking the two-degree-of-freedom undamped vibration discrete model as an example, the mass matrix [M] is:

[0119]

[0120] The stiffness matrix [K] is:

[0121]

[0122] Substitute the mass matrix [M] and stiffness matrix [K] into [K]{x}=ω 2 [M]{x}, we can get

[0123]

[0124] Multiply both sides of the above formula by [M] -1 We can get:

[0125]

[0126] Solve the matrix [M] -1 The eigenvalues ​​and eigenvectors of [K], whose eigenvalue is ω i 2 (i=1, 2), ω i is the natural angular frequency, natural frequency f = ω i / 2π.

[0127] Eigenvalue ω i 2 The corresponding eigenvector {x} i is the vibration shape corresponding to the natural frequency f.

[0128] After discretization, the longitudinal vibration mode of the welding head model is the 12th order mode, and the natural frequency of this order is 20271 Hz, which meets the tracking frequency range of the ultrasonic generator and does not require structural optimization.

[0129] Example 2:

[0130] The welding head designed in this embodiment is made of 45# steel, the rated power of the ultrasonic welding machine is 800W (low power working condition), the operating frequency f is 28KHz, the frequency tracking range of the ultrasonic generator is ±300Hz, the output end diameter of the amplitude transformer D=24mm, the amplitude amplification factor is 2, and the transition surface segment is a "~" shaped surface.

[0131] This embodiment provides a method for designing a welding head suitable for ultrasonic continuous welding, including the following steps:

[0132] S1. Determine the dimensions of the input and output sections of the welding head body: The cross-section of the welding head body is rectangular. The width of the input section w0 and the thickness of the welding head body d are both equal to the diameter D of the output end of the horn. The width of the output section w1 depends on the amplitude magnification factor. When the amplitude magnification factor is N, w1 = w0 / N.

[0133] That is, w0=d=24mm; w1=w0 / 2=12mm.

[0134] S2. Determine the length of the welding head body: Calculate the wavelength of the ultrasonic wave transmitted by the welding head based on its material properties, and determine the length l of the welding head body, the length l1 of the input section, the length l2 of the transition surface section, and the length l3 of the output section. Where l is half of the ultrasonic wave length, i.e. l ​​= λ / 2. The relationship between the length l1 of the input section, the length l2 of the transition surface section, and the length l3 of the output section is: l1 = l3 = l2 / 2 = λ / 8.

[0135] In this embodiment, the Young's modulus of 45# steel is E=200 GPa, and the density is ρ=7850 kg / m 3 , the ultrasonic sound speed c can be solved by the following formula:

[0136]

[0137] The calculated value c = 5047.5 m / s, and the ultrasonic wavelength λ can be solved by the following formula:

[0138]

[0139] It is calculated that λ=0.18m, the welding head length l is half of the ultrasonic wavelength, that is, l=90mm, and the relationship between the input section length l1, the transition surface section length l2, and the output section length l3 is: l1=l3=l2 / 2=λ / 8, that is, l1=l3=22.5mm, l2=45mm.

[0140] S3. Select the transition curve nodes of the transition surface segment: Considering the size of the input and output segments of the welding head and the stability of vibration transmission, since the welding head body is an axisymmetric structure, select n nodes (n ≥ 4) required for the "~"-shaped transition curve on one side of the transition surface segment;

[0141] In step S3, a rectangular coordinate system is established with the geometric center of the cross section at the end of the welding head input section as the origin. The horizontal coordinate of the end node is determined by the length of the transition surface section, and the vertical coordinate of the node is determined by the width of the welding head input section and output section.

[0142] When w0 = 24 mm, w1 = 12 mm, l1 = l3 = 22.5 mm, and l2 = 45 mm, nodes A (22.5, 12) and E (67.5, 6) are determined from the transition surface area, and the midpoint of segment AE is selected as node C (45, 9). To ensure stable energy transmission and uniform vibration distribution during welding, all nodes are equally spaced and symmetrical around the center of node C. Therefore, nodes B (33.75, 11) and D (56.25, 7) are selected.

[0143] S4. Calculate the transition curve expression: Use the least squares method to fit a cubic polynomial to perform curve fitting on the five nodes selected in step S3 to obtain the transition curve expression h(x) on one side of the transition surface segment;

[0144] The key to generating the "~"-shaped transition surface segment in this embodiment is to design and calculate the corresponding transition curve. Therefore, this embodiment performs detailed calculations to obtain the curve equation h(x). In this embodiment, the five nodes taken are:

[0145] A: x0=22.5, h(x0)=12; B: x1=33.75, h(x1)=11; C: x2=45, h(x2)=9;

[0146] D: x3=56.25, h(x3)=7; E: x4=67.5, h(x4)=6;

[0147] Assume that the fitting cubic polynomial is h(x)=a0+a1x+a2x 2 +a3x 3 , the canonical equations are:

[0148]

[0149] When n=5, we can calculate:

[0150]

[0151]

[0152]

[0153] Substituting the above results into the canonical equations, we get:

[0154]

[0155] The solution is:

[0156] a0=7, a1=0.5185, a2=-0.0158, a3=0.00011706,

[0157] The cubic polynomial curve expression can be obtained:

[0158] h(x)=7+0.5185x-0.0158x 2 +0.00011706x 3 x∈(22.5,67.5).

[0159] S5. Construct a piecewise function of the cross-sectional area of ​​the welding head body in the longitudinal direction: construct a piecewise function H(x) of the width of one side of the welding head body according to the dimensional parameters w0, w1, l, l1, l2 obtained in steps S1 and S2 and the cubic polynomial curve h(x) obtained in step S4;

[0160]

[0161] Symmetrically transform the width piecewise function H(x) along the x-axis to obtain the width piecewise function -H(x) on the symmetric side;

[0162]

[0163] Therefore, the overall width function of the welding head body W(x)=2H(x), that is,

[0164]

[0165] Then the area enclosed by W(x) and d is the cross-sectional function S(x) along the length direction of the welding head body, that is,

[0166]

[0167] Where x∈[0,l1) refers to the cross-section set of the input section along the length of the welding head body; x∈(l1,l1+l2) refers to the cross-section set of the transition section along the length of the welding head body; x∈

[0168] (l1+l2,l] refers to the cross-section set of the welding head body along the length direction at the output end;

[0169] In this embodiment, specifically:

[0170]

[0171]

[0172] Therefore, the overall width function of the welding head body W(x)=2H(x), that is,

[0173]

[0174] Then the area enclosed by W(x) and d is the cross-sectional function S(x) along the length direction of the welding head body, that is,

[0175]

[0176] S6, forming the welding head body: superimposing the longitudinal cross-section segments of the welding head body obtained in step S5 along the longitudinal direction, such as Figure 5 As shown, the welding head body is obtained under low power working conditions.

[0177] Furthermore, it is determined whether the welding head body obtained in step S6 meets the frequency tracking range of the ultrasonic generator: a model of the obtained welding head body is established for modal analysis to solve the natural frequency of the longitudinal vibration mode of the welding head body. If the natural frequency is within the frequency tracking range of the ultrasonic generator, no structural optimization is required; if the natural frequency is not within the frequency tracking range of the ultrasonic generator, structural optimization is required.

[0178] In this embodiment, the longitudinal vibration mode of the welding head model obtained through discretization is the 12th order mode, and the natural frequency of this order is 28399 Hz. The natural frequency of the welding head model is greater than the tracking frequency range of the ultrasonic generator, and structural optimization is required.

[0179] Welding head structure optimization: Because the natural frequency f is related to the stiffness matrix [K] and the mass matrix [M], the natural frequency of the welding head can be further controlled by properly adjusting the dimensions of l1 and l3 to control the welding head mass.

[0180] In this embodiment, a modal analysis is performed on the optimized welding head model. When l1=20 mm and l3=25 mm, its longitudinal vibration mode is the 12th order mode, and the natural frequency of this order is 28049 Hz, which meets the tracking frequency range of the ultrasonic generator.

[0181] The embodiments of the present invention are described in detail above, but the contents described are only preferred embodiments of the present invention and should not be considered to limit the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of this patent.

Claims

1. A method for designing a welding head suitable for ultrasonic continuous welding, characterized by: The welding head includes a welding head body, the welding head body includes an input section, a transition surface section and an output section, the cross section of the welding head body in the length direction is rectangular, and the welding head body is an integrally formed structure; the cross-sectional area function of the welding head body in the length direction is: ； Where, S ( x ) is the cross-sectional area of ​​the welding head body in the length direction, w 0 is the input segment width, w 1 is the output segment width, d is the thickness of the welding head body, l 1 is the input segment length, l 2 is the length of the transition surface segment, h ( x ) is the transition curve function of the transition surface segment, l The length of the welding head body; the two sides of the output section of the welding head body perpendicular to the welding direction are set to be chamfered; The design method of the welding head comprises the following steps: S1. Determine the size of the input section and output section of the welding head body: the width of the input section of the welding head body w 0 and welding head body thickness d The same as the output end diameter of the horn D Equal; when the amplitude magnification factor is N hour, w 1= w 0 / N; S2. Determine the length of the welding head body: Calculate the wavelength of the ultrasonic wave it transmits based on the material properties of the welding head body λ , determine the length of the welding head body l , input segment length l 1. Transition surface segment length l 2 and the output segment length l 3; S3. Select the transition curve node of the transition surface segment: Select the transition curve node required on one side of the transition surface segment. n nodes, n ≥4; S4, calculate the transition curve expression: use the least squares method to fit the cubic polynomial selected in step S3 n Nodes are used for curve fitting to obtain the transition curve expression on one side of the transition surface segment h ( x ); S5. Construct a piecewise function of the cross-sectional area in the longitudinal direction of the welding head body: according to the size parameters obtained in steps S1 and S2 w 0. w 1. l 、 l 1. l 2 and the cubic polynomial curve obtained in step S4 h ( x ) Construct a piecewise function of the width of one side of the welding head body H ( x ): ； Split the width into piecewise functions H ( x )along x Axis symmetry, the width of the symmetric side is obtained as a piecewise function - H ( x ): ； Get the overall width of the welding head body W(x) =2 H(x) : ； but W ( x )and d The enclosed area is the cross-sectional area of ​​the welding head body in the length direction S ( x ): Where, x ∈[ 0,l 1 ) refers to the cross-section set along the length direction of the welding head body of the input section; x ∈( l 1 , l 1 + l 2 ) refers to the cross-section set of the transition surface section along the length direction of the welding head body; x ∈( l 1 + l 2 , l ] refers to the cross-section set along the length direction of the welding head body at the output end; S6. Forming a welding head body: superimposing the longitudinal cross-sections of the welding head body obtained in step S5 along the longitudinal direction to obtain a welding head body.

2. The method for designing a welding head suitable for ultrasonic continuous welding according to claim 1, characterized in that: In step S2, l is half the wavelength of ultrasound. l = λ / 2, input segment length l 1. Transition surface segment length l 2. Output segment length l The relationship between the 3 is: l 1= l 3= l 2 / 2= λ / 8。 3. The method for designing a welding head suitable for ultrasonic continuous welding according to claim 1, characterized in that: In step S3, a rectangular coordinate system is established with the geometric center of the cross section at the end of the input segment as the origin, the end node coordinates are determined by the length of the transition surface segment, the node abscissa is determined by the length of the welding head body; the node ordinate is determined by the width of the welding head input segment and output segment.

4. The method for designing a welding head suitable for ultrasonic continuous welding according to claim 1, characterized in that: Determine whether the welding head body obtained in step S6 meets the frequency tracking range of the ultrasonic generator: establish a model of the obtained welding head body for modal analysis, and solve the natural frequency of the longitudinal vibration mode of the welding head body. If the natural frequency is within the frequency tracking range of the ultrasonic generator, no structural optimization is required; if the natural frequency is not within the frequency tracking range of the ultrasonic generator, structural optimization is required.

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