Interface welding unit material reduction design method of fusion welding technology

Abstract

The invention discloses an interface welding unit material reduction design method of a fusion welding technology. According to the method, an electro-thermal coupling simulation model of the welding interface is established, temperature field distribution of the welding interface is obtained through calculation according to the heat conduction theory, material reduction is conducted on a welding unit, the cross sectional area of a supercooled area of the temperature field is reduced, and a superheated area of the temperature field is directly cut off; the uniformity of a temperature field of a welding interface and the co-melting area of a weldment interface can be improved, the heat efficiency of a welding unit is improved, and the target temperature can be reached more quickly under the same power; a higher interface temperature interval can be realized under the same input current and heating duration; the method is suitable for regulating and controlling a special-shaped weld joint welding interface temperature field and meets different process environment requirements; the design method is simple and convenient, the designed welding unit is simple in manufacturing process, the process efficiency is improved, the cost is reduced, and the method is suitable for batch automatic production.

Description

Technical Field

[0001] The invention relates to the molding connection of plastics, and in particular to a material reduction design method for an interface welding unit of a meltable composite material welding technology. Background Art

[0002] Thermoplastic composites have excellent mechanical properties such as high damage tolerance, good fracture toughness and impact resistance. The phase change characteristics of their molding process give their structural parts advantages in secondary processing, melt repair and recycling. They have been increasingly used in aerospace, automotive and rail transportation fields.

[0003] Resistance welding of thermoplastic composites utilizes a welding unit (a heat-generating sheet or mesh conductor, such as a wire mesh) to generate Joule heat to heat the upper and lower weldment components. This heat melts the polymer at the weldment interface. The molten polymer then diffuses and fuses under appropriate compressive stress (interfacial contact pressure), then cools and crystallizes, achieving interfacial welding of the composite materials. Controlling the temperature field at the weld interface affects the polymer melt area and crystallization state, and is crucial to weld quality.

[0004] The meltability of thermoplastic composites makes their structural interfaces weldable, leading to the development of numerous welding processes (Ginger Gardiner, Welding thermoplastic composites, Composites World, 2023). Resistance welding, among other techniques, is widely used in industry for its low cost, high efficiency, and excellent connection quality. The quality of thermoplastic composite interface welds depends on the crystallization behavior of the various phases at the weld. The interface weld unit and the temperature field during the welding process determine key properties such as interface strength.

[0005] A large number of studies have shown that for single lap welding, adjusting the welding process parameters when the welding unit is determined can achieve a relatively uniform gradient temperature field. However, for continuous welding, especially welding with special-shaped interfaces, further in-depth research and improvement of the welding process are still needed. How to achieve interface temperature field control is the key. At the same time, Koutras et al., Composites: Part A, Vol. 105, pp. 57-67, 2018 proposed that for stainless steel welding units, interface failure is manifested as fiber / matrix interface debonding rather than stainless steel / matrix interface failure, indicating that the main factor determining the quality of the weld joint is the fiber / matrix interface strength. This is because traditional sheet welding units will cut off the weld interface, and the upper and lower weld interface materials are not only difficult to fuse together at the weld, but also there is a serious imbalance of interface residual compressive stress after welding. In addition, a large number of studies have pointed out that the welding interface temperature field has a non-uniform distribution in the transverse direction (perpendicular to the potential direction within the welding interface), resulting in initial defects such as welding gaps at the transverse ends of the weld, affecting the welding quality. Therefore, it is particularly important to improve the welding interface quality between welds based on the design of the welding unit. Summary of the Invention

[0006] In response to the problems of difficulty in regulating the welding temperature field of the special-shaped interface in the existing welding unit and difficulty in fusion of the welding interface at the weld, the present invention proposes a subtractive design method for the special-shaped interface welding unit, which can not only achieve the uniformity adjustment of the gradient temperature field of the special-shaped interface welding, but also increase the contact area of ​​the weldment at the weld to promote fusion of the welding interface, thereby improving the welding quality.

[0007] When welding the upper weldment and the lower weldment, the welding unit is placed at the welding interface between the upper weldment and the lower weldment, and electrode interfaces are set at both ends of the welding unit. The two electrode interfaces are connected to an external DC power supply, and current is input through the DC power supply; the input power is adjusted by controlling the input current, the welding unit is heated, and the heat is transferred to the upper weldment and the lower weldment, causing the material at the interface to melt; the melting and crystallization state of the welding interface is controlled by controlling the heating time and cooling rate, so that the upper weldment and the lower weldment are welded together.

[0008] The interface welding unit subtractive design method of the present invention comprises the following steps:

[0009] 1) Establish an electrothermal-mechanical coupling simulation model:

[0010] Based on the composite material resistance welding process operation platform, an electric, thermal and mechanical coupling simulation model of the welding interface is established to effectively simulate the heat conduction of the welding process and solve the temperature field distribution of the welding interface;

[0011] 2) Get the temperature field distribution:

[0012] The current flows through the welding unit, causing the welding unit to heat up. Based on the electro-thermal-mechanical coupling simulation model and heat conduction theory, the temperature field distribution of the welding interface is calculated;

[0013] 3) Material reduction in welding unit:

[0014] When the input current is fixed, the temperature field distribution of the welding interface is controlled by adjusting the cross-sectional area of ​​the welding unit through which the current flows. Based on the temperature field distribution of the welding interface, the welding unit is reduced in material: the cross-sectional area of ​​the area where the temperature field is too cold is reduced, thereby reducing the cross-sectional area through which the current flows to increase the heating power; the area where the temperature field is too hot is directly cut off.

[0015] 4) Model modification:

[0016] The welding unit after material reduction is replaced with the welding unit in the original electrothermal-mechanical coupling simulation model. Steps 2) and 3) are repeated. The material reduction area is adjusted with the interface welding allowable temperature range as the goal until the desired temperature field distribution is obtained. The welding unit at this time is the desired welding unit, and the geometric parameters of the corresponding welding unit are obtained.

[0017] The welding unit after material reduction increases the contact and fusion area of ​​the welding interface. The welding interfaces of the upper and lower weldments at the material reduction are in direct contact. On the basis of a more uniform temperature field, the contact area at the weld is increased, which promotes the fusion of the welding interface and improves the welding quality.

[0018] In addition, the cross-sectional area of ​​the welding unit after the current flows through the material reduction becomes smaller, the heating efficiency is improved when the current remains unchanged, the heating time required to reach the same temperature range is shortened, and the welding efficiency is improved.

[0019] In step 1), the electrothermal-mechanical coupling simulation model of the welding interface includes an upper weldment, a lower weldment, a welding unit, and an electrode interface. Input parameters include material parameters of the weldment and welding unit, weld interface morphology parameters, welding unit geometry parameters, weld interface contact pressure, weld interface heat exchange coefficient, electrode clamping distance, current, and heating and cooling times. The lower surface of the lower weldment is fixed, and both ends of the welding unit are set as electrode interfaces, with one end at zero potential and the other end inputting current.

[0020] In step 2), according to the heat conduction theory, the two-dimensional heat conduction equation of the welding unit at the welding interface is:

[0021]

[0022] Where ρ is the density, C p is the specific heat capacity, κ xx , κ xy and κ yyare the anisotropic thermal conductivity of the welding unit in the x-direction, xy-direction and y-direction, is the heat power per unit volume; and:

[0023]

[0024] The last two terms on the right side of the equation are related to material melting and crystallization, which depend on the materials of the upper and lower weldments. is the heat of fusion, It is the heat of crystallization; is the Joule heat, which is a controllable item related to the welding unit and input power, and has:

[0025]

[0026] Among them, U and I represent the voltage and input current at both ends of the welding unit, V ele and S ele represent the volume and cross-sectional area of ​​the welding unit, ρ R It is known from the above formula that when the input current is fixed, the temperature field distribution of the welding interface is adjusted by adjusting the cross-sectional area S of the welding unit through which the current flows. ele To regulate.

[0027] In step 3), for the rectangular welding unit, the temperature field distribution is ellipsoidal (multi-ellipsoidal) shaped, and the temperature field distribution is often uneven, which will lead to the situation where the horizontal middle temperature is too high and the end temperature is too low. For the rectangular welding unit, in order to enhance the heating power of its horizontal end grid, the present invention starts to reduce the material from the central area of ​​the welding unit to form a plurality of series-parallel resistors. By cutting at different positions, the connection relationship of each resistor is changed, thereby changing the series-parallel relationship to form a plurality of resistors parallel to each other. The adjacent resistors are connected end to end in sequence to finally form a horizontal series subtractive welding unit; each resistor forms an elongated elliptical horizontal unit temperature field, and the connecting parts at both ends respectively form an elliptical longitudinal (parallel to the potential direction in the welding interface) unit temperature field. The superimposed temperature fields at both ends make the overall distribution of the temperature field at the welding interface more uniform; the horizontal series subtractive welding unit obtains a more uniform interface temperature field than the conventional welding unit by superimposing the end heat source; the subtractive unit designed by the present invention achieves weight reduction while increasing the welding interface contact area of ​​the upper and lower weldments, which is conducive to promoting interface fusion during the welding process.

[0028] The present invention can handle conventional rectangular welds and various special-shaped welds, such as broken-line welds or hyperbolic welds, and realizes optimized design of welding units.

[0029] For complex welds, secondary development can be performed in step 3) by combining topology optimization or machine learning to prioritize subtractive design of welding units in overheated areas of the welding interface temperature field.

[0030] Advantages of the present invention:

[0031] The present invention adopts a subtractive design for the welding unit, which can improve the uniformity of the temperature field of the welding interface and the fusion area of ​​the weldment interface, thereby improving the thermal efficiency of the welding unit, and can reach the target temperature faster under the same power; a higher interface temperature range can be achieved under the same input current and heating time; it is suitable for regulating the temperature field of the welding interface of special-shaped welds and meeting the requirements of different process environments; the design method of the present invention is simple, the manufacturing process of the designed welding unit is simple, the process efficiency is improved and the cost is reduced, and it is suitable for batch automated production. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A schematic diagram of an electro-thermal-mechanical coupling simulation model of an embodiment of a subtractive design method for an interface welding unit according to the present invention;

[0033] Figure 2 A comparison diagram of a transverse series subtractive welding unit obtained by the interface welding unit subtractive design method of the present invention and a conventional welding unit;

[0034] Figure 3 for Figure 2 Temperature field distribution diagram of single lap welding interface corresponding to each welding unit in;

[0035] Figure 4 The temperature field distribution diagram of different welding units corresponding to the broken line special-shaped weld obtained by the interface welding unit subtractive design method of the present invention;

[0036] Figure 5 The interface temperature field cloud maps of the broken line special-shaped weld corresponding to different welding units and the cross-sectional temperature field cloud maps of the weldment at the interface obtained according to the interface welding unit subtractive design method of the present invention, wherein (a) is the interface cross-sectional temperature field cloud map of the conventional welding unit, (b) is the interface temperature field cloud map of the series-parallel welding unit, (c) is the interface temperature field cloud map of the longitudinal end optimization-series welding unit, (d) is the cross-sectional temperature field cloud map of the weldment at the interface of the conventional welding unit, (e) is the cross-sectional temperature field cloud map of the weldment at the interface of the series-parallel welding unit, and (f) is the cross-sectional temperature field cloud map of the weldment at the interface of the longitudinal end optimization-series welding unit;

[0037] Figure 6 The flowchart of one embodiment of the interface welding unit subtractive design method of the present invention. DETAILED DESCRIPTION

[0038] The present invention will be further described below through specific embodiments in conjunction with the accompanying drawings.

[0039] like Figure 1 As shown, when welding the upper and lower parts, a welding unit is placed at the welding interface between the upper and lower parts. Electrode interfaces are provided at both ends of the welding unit, and the two electrode interfaces are connected to an external DC power supply, which inputs current. By controlling the input current and adjusting the input power, the welding unit is heated, and the heat is transferred to the upper and lower parts, causing the material at their interface to melt. By controlling the heating time and cooling rate, the melting and crystallization state of the welding interface is controlled, thereby welding the upper and lower parts together. The welding unit is a heat-generating sheet or mesh conductor, such as a wire mesh.

[0040] The interface welding unit subtractive design method of the present invention is as follows: Figure 6 As shown, the following steps are included:

[0041] 1) Establish an electrothermal-mechanical coupling simulation model:

[0042] Based on the composite material resistance welding process operation platform, an electric, thermal and mechanical coupling simulation model of the welding interface is established to effectively simulate the heat conduction of the welding process and solve the temperature field distribution of the welding interface;

[0043] The electrothermal-mechanical coupling simulation model includes the upper weldment, the lower weldment, the welding unit and the electrode interface; the input parameters include the material parameters of the weldment and the welding unit, the welding interface morphology parameters, the geometric parameters of the welding unit, the welding interface contact pressure p, the heat exchange coefficient of the welding interface, and the electrode clamping distance L. c , input current I, heating and cooling time; the lower surface of the lower weldment is fixed, and the electrode interfaces at both ends of the welding unit are set to zero potential at one end and input current at the other end;

[0044] 2) Get the temperature field distribution:

[0045] The current flows through the welding unit, and the welding unit heats up. Based on the electric, thermal and mechanical coupling simulation model and the heat conduction theory, the two-dimensional heat conduction equation of the welding unit at the welding interface is:

[0046]

[0047] Where ρ is the density of the welding unit, C p is the specific heat capacity of the welding unit, κ xx , κ xy and κ yy are the anisotropic thermal conductivities corresponding to the x, xy, and y directions of the welding unit, is the heat power per unit volume; and:

[0048]

[0049] Among them, the last two terms on the right side of the equal sign are related to material melting and crystallization, which depend on the materials of the upper and lower weldments.

[0050] is the heat of fusion, It is the heat of crystallization; It is Joule heat, which is related to the welding unit and input power. It can be controlled by controlling the input power and changing the geometric parameters of the welding unit.

[0051]

[0052] Among them, U and I represent the voltage and input current at both ends of the welding unit, V ele and S ele represent the volume and cross-sectional area of ​​the welding unit, ρ R represents the resistivity of the welding unit (considered as a constant in the welding interface area); from the above formula, when the input current is fixed, the temperature field distribution of the welding interface is adjusted by adjusting the cross-sectional area S of the welding unit through which the current flows. ele to regulate;

[0053] 3) Material reduction in welding unit:

[0054] When the input current is fixed, the temperature field distribution of the welding interface is controlled by adjusting the cross-sectional area of ​​the welding unit through which the current flows. Based on the temperature field distribution of the welding interface, the welding unit is reduced in material: the cross-sectional area of ​​the area where the temperature field is too cold is reduced, thereby reducing the cross-sectional area through which the current flows to increase the heating power; the area where the temperature field is too hot is directly cut off.

[0055] For rectangular welding units such as Figure 2 As shown in the left figure, the temperature field distribution is ellipsoidal. The temperature field distribution is often uneven, which will lead to the situation that the temperature in the middle of the horizontal direction is too high and the temperature at the end is too low. For the rectangular welding unit, in order to enhance the heating power of the grid at its horizontal end, the present invention starts to reduce the material from the center area of ​​the welding unit to form multiple series-parallel resistors. By cutting at different positions, the connection relationship of each resistor is changed, thereby changing the series-parallel relationship to form multiple parallel resistors. The adjacent resistors are connected end to end in sequence, and finally a horizontal series subtractive welding unit is formed. Figure 2 As shown in the middle figure, each resistor forms an elongated elliptical transverse unit temperature field, and the connecting parts at both ends form an elliptical longitudinal unit temperature field. Figure 2As shown in the figure on the right, at both ends of the horizontal direction, the horizontal unit temperature field and the vertical unit temperature field are superimposed, making the overall distribution of the temperature field at the welding interface more uniform. The horizontal series subtractive welding unit achieves a more uniform interface temperature field than conventional welding units by superimposing the end heat sources. The subtractive unit designed in this invention reduces weight while increasing the contact area of ​​the welding interface between the upper and lower weldments, which is conducive to promoting interface fusion during the welding process.

[0056] 4) Model modification:

[0057] The welding unit after material reduction is replaced with the welding unit in the original electrothermal-mechanical coupling simulation model. Steps 2) and 3) are repeated. The material reduction area is adjusted with the interface welding allowable temperature range as the goal until the desired temperature field distribution is obtained. The welding unit at this time is the desired welding unit, and the geometric parameters of the corresponding welding unit are obtained.

[0058] The welding unit after material reduction increases the contact and fusion area of ​​the welding interface. The welding interfaces of the upper and lower weldments at the material reduction are in direct contact. On the basis of a more uniform temperature field, the contact area at the weld is increased, which promotes the fusion of the welding interface and improves the welding quality.

[0059] In addition, the cross-sectional area of ​​the welding unit after the current flows through the material reduction becomes smaller, the heating efficiency is improved when the current remains unchanged, the heating time required to reach the same temperature range is shortened, and the welding efficiency is improved.

[0060] In this embodiment, the welding interface is 25mm×25mm, the allowable welding temperature range is 130~160℃, the unit subtraction width of the 80-mesh stainless steel mesh welding unit is 0.5mm, the longitudinal reserved width of the end is 1.95mm, and the heating is performed for 66s at an input current of 20A. The transverse series subtractive welding unit designed by the present invention obtains a more uniform interface temperature field than the conventional welding unit by superimposing the end heat source. Figure 2 In contrast, the subtractive welding unit designed in the present invention reduces weight while increasing the contact area of ​​the welding interface between the upper and lower weldments, which is beneficial to promoting interface fusion during the welding process.

[0061] Comparison of temperature field distribution between tandem subtractive welding unit and conventional welding unit under the same input power Figure 3 The results show that when the temperature reaches the same range of 130-160℃, the transverse series subtractive welding unit ( Figure 3 The time required for the conventional welding unit ( Figure 3 The center area of ​​the left figure is overheated, and the lateral end area is too cold. In addition, under the same input current and heating time, the temperature field of the overlap area of ​​the conventional welding unit is 110-160℃ when heating for 99s, and the horizontal series subtractive welding unit ( Figure 3The temperature range of the welding unit (right figure) is increased to 180-230℃, indicating that under the same input current and heating time, the heating efficiency of the transverse series subtractive welding unit is higher and it can be applied to materials with a higher allowable temperature range.

[0062] like Figure 4 The following is a typical case of special-shaped welds. For a broken line weld, the heating time is 99s at an input current of 20A. The conventional welding unit ( Figure 4 The temperature range of the left figure is 170-537℃, with a difference of 367℃; the series-parallel subtractive welding unit designed by the present invention ( Figure 4 The temperature range of the series-parallel subtractive welding unit is 230-391°C, with a difference of 161°C. The series-parallel subtractive welding unit adopts series resistors in the upper and lower parts along the longitudinal direction with the broken line weld corner as the midline, and the upper and lower series resistors are connected in parallel at the transverse ends; in order to further improve the heating power of the transverse end, based on the further optimization of the present invention, the transverse end parallel design is cancelled, and the end resistors at both ends of the longitudinal direction are optimized by S-type subtraction to form a series resistor. The two ends of the series resistor are connected to the electrode interface respectively, corresponding to Figure 4 At the upper and lower ends of the right side of the right figure, the designed longitudinal end optimization-series subtractive welding unit ( Figure 4 The temperature range of the right figure is 234~339℃, with a difference of 105℃. The allowable temperature field range of the broken line weld is set to 220~330℃. The cross-sectional temperature field cloud diagrams of the welding interface corresponding to the above three types of welding units are shown as follows: Figure 5 ;like Figure 5 As shown in (c) and (f), the longitudinal end optimization-tandem subtractive welding unit achieves the desired temperature field.

[0063] Finally, it should be noted that the purpose of disclosing the embodiments is to facilitate a further understanding of the present invention. However, those skilled in the art will appreciate that various substitutions and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the contents disclosed in the embodiments; the scope of protection claimed by the present invention shall be determined by the scope defined in the claims.

Claims

1. A subtractive design method for an interface welding unit, characterized in that: The design method comprises the following steps: 1) Establish an electrothermal-mechanical coupling simulation model: Based on the composite material resistance welding process operation platform, an electric, thermal and mechanical coupling simulation model of the welding interface is established to effectively simulate the heat conduction of the welding process and solve the temperature field distribution of the welding interface; 2) Get the temperature field distribution: The current flows through the welding unit, causing the welding unit to heat up. Based on the electro-thermal-mechanical coupling simulation model and heat conduction theory, the temperature field distribution of the welding interface is calculated; 3) Material reduction in welding unit: When the input current is fixed, the temperature field distribution of the welding interface is controlled by adjusting the cross-sectional area of ​​the welding unit through which the current flows. Based on the temperature field distribution of the welding interface, the welding unit is reduced in material: the cross-sectional area of ​​the area where the temperature field is too cold is reduced, thereby reducing the cross-sectional area through which the current flows to increase the heating power; the area where the temperature field is too hot is directly cut off. 4) Model modification: Replace the welding unit in the original electro-thermal-mechanical coupling simulation model with the welding unit after material reduction, and repeat steps 2) and 3). With the interface welding allowable temperature range as the goal, adjust the material reduction area until the required temperature field distribution is obtained. The welding unit at this time is the required welding unit, and the geometric parameters of the corresponding welding unit are obtained; The welding unit after material reduction increases the contact and fusion area of ​​the welding interface. The welding interfaces of the upper and lower weldments at the material reduction are in direct contact. On the basis of a more uniform temperature field, the contact area at the weld is increased, which promotes the fusion of the welding interface and improves the welding quality. In addition, the cross-sectional area of ​​the welding unit after the current flows through the material reduction becomes smaller, the heating efficiency is improved when the current remains unchanged, the heating time required to reach the same temperature range is shortened, and the welding efficiency is improved.

2. The design method according to claim 1, wherein: In step 1), the electrothermal-mechanical coupling simulation model of the welding interface includes an upper weldment, a lower weldment, a welding unit, and an electrode interface; the input parameters include material parameters of the weldment and the welding unit, welding interface morphology parameters, geometric parameters of the welding unit, welding interface contact pressure, heat exchange coefficient of the welding interface, electrode clamping distance, current, heating and cooling time.

3. The design method according to claim 1, wherein: In step 1), in the electrothermal-mechanical coupling simulation model of the welding interface, the lower surface of the lower weldment is fixed, and both ends of the welding unit are set as electrode interfaces, one end is at zero potential, and the other end is input with current.

4. The design method according to claim 1, wherein: In step 2), the input current is fixed, and the temperature field distribution of the welding interface is controlled by adjusting the cross-sectional area of ​​the welding unit through which the current flows.

5. The design method according to claim 1, wherein: In step 3), material is reduced starting from the center area of ​​the welding unit to form a plurality of resistors connected in series and parallel. By cutting at different positions, the connection relationship of each resistor is changed, thereby changing the series and parallel relationship.

6. The design method according to claim 1, wherein: Applicable to conventional rectangular welds and various special-shaped welds.

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