Method of controlling welding distortion with auxiliary heat source

Abstract

The application relates to a method for controlling welding deformation by an auxiliary heat source, which comprises the following steps: simulating a welding process without an auxiliary heat source and simulating a welding process with a determined auxiliary heat source by using general finite element software, and selecting an existing heat source model to calculate a temperature field; according to the calculation result of the temperature field, selecting a peak temperature range from a melting point temperature to 100 DEG C as an auxiliary heat source application range; assembling and fixing materials to be welded, and heating the auxiliary heat source application range before a welding heat source, and when the temperature of a workpiece in the heating range reaches a specified preheating temperature, the assembled welding materials can be welded. 8 / 5 The method can control the welding angle deformation of materials under the premise that no structure transformation and heat affected zone control occur, and can reduce the t The method has good preheating effects on welding structures of various sizes.

Description

[0001] Technology Neighborhood

[0002] This invention relates to the field of welding technology, and more specifically to a method for controlling welding deformation using an auxiliary heat source. Background Technology

[0003] Due to the concentrated heat source during welding, the material is locally heated or melted, creating a significant temperature gradient within the welded structure. As the heated material expands due to thermal expansion and contraction, it is constrained by the unheated metal, resulting in compressive plastic strain. Conversely, as the heated material gradually cools, the resulting contraction is also constrained by the surrounding material, leading to elastic strain or even plastic strain. The uneven heating and cooling of the material during welding inevitably causes residual stress and deformation within the welded structure. Weld angular deformation, in particular, arises from the uneven transverse contraction of the welding material in the thickness direction.

[0004] Significant welding deformation can have a substantial impact on the use and assembly of welded structures, making its control crucial. Current measures for controlling welded structural deformation can be categorized into pre-weld, during-weld, and post-weld measures. Pre-weld measures include preheating, rational design of the welding process and structure, and pre-deformation. During-weld measures include reducing heat input to the weld, rationally arranging the assembly and welding sequence, and pre-stretching. Post-weld measures utilize mechanical and heating methods. While these methods can reduce residual welding stress and deformation to some extent, they also have drawbacks. For example, preheating is particularly demanding for larger components, requiring extensive preheating time. Adding auxiliary heat sources, however, allows for localized heating of the welded structure, significantly improving preheating efficiency. Furthermore, for large welded components, preheating during welding is of paramount importance for controlling weld angular deformation.

[0005] For ultra-high strength steel, due to its high strength level, it is highly sensitive to diffusible hydrogen and hardened microstructure during welding, easily leading to hydrogen-induced delayed fracture, which greatly affects the welded component. Therefore, controlling the hydrogen content during welding and reducing hydrogen sulfide (TH) during cooling are crucial. 8 / 5 Controlling cold cracking in ultra-high strength steel is extremely crucial. Adding an auxiliary heat source can effectively reduce the temperature gradient along the thickness of the plate, thereby controlling angular deformation and reducing t. 8 / 5 This has practical significance for welding ultra-high strength steel.

[0006] There are some research results on auxiliary heat sources both domestically and internationally, but most of them combine two welding methods, such as using laser welding on the front side and argon arc welding on the back, or laser welding combined with laser welding. This method can reduce the internal temperature gradient of the welded structure, thereby better controlling welding deformation. However, if the heat input of the heat source is too large, the metal around the weld will prematurely enter the plastic state. For some high-strength materials with easily transformable microstructures, this can lead to a series of defects such as cold cracking and an excessively large heat-affected zone, which is detrimental to the service life of the welded structure. Summary of the Invention

[0007] In view of the above-mentioned problems in the existing technology, the technical problem to be solved by the present invention is: how to compensate for the angular deformation generated in the welding of high-strength steel thin plates.

[0008] To solve the above technical problems, the present invention adopts the following technical solution: a method for controlling welding deformation with an auxiliary heat source, comprising the following steps:

[0009] The precise shape and size of the workpiece are obtained through 3D scanning. A 3D geometric model with the same shape and size is established and meshed. The meshed model is then imported into a general finite element software. The model is assigned relevant material parameters, the initial temperature and ambient temperature of the welding process are defined, the weld and welding path are defined according to the actual welding situation, and the temperature field is calculated using an existing heat source model. Based on the temperature field calculation results, the range of peak temperature from the melting point to 100℃ is selected as the range for applying auxiliary heat source.

[0010] The materials to be welded are assembled and fixed. The deformation of the workpiece after assembly is measured with a ruler to obtain initial deformation data. The moving flame heating device is moved along the welding direction on the welding path. An auxiliary heat source heats the area of ​​the auxiliary heat source before the welding heat source. When the temperature of the workpiece within the heating area reaches the specified preheating temperature, the assembled materials can be welded.

[0011] After welding and cooling, the deformation of the welded material is recorded and compared with the initial deformation to obtain the overall deformation.

[0012] Preferably, the general-purpose finite element software used is MSC.MARC, Abaqus, or ANSYS.

[0013] Preferably, the auxiliary heat source is a flame torch that follows the welding torch for heating.

[0014] Compared with the prior art, the present invention has at least the following advantages:

[0015] This method provides a cost-effective auxiliary heat source preheating method for local preheating and on-the-fly preheating of welded components. This method can reduce weld angular deformation while controlling the material's microstructure transformation and the heat-affected zone, and can also reduce the time required for welding cooling. 8 / 5 It has a good preheating effect on welded structures of various sizes. Attached Figure Description

[0016] Figure 1 This is a finite element mesh diagram.

[0017] Figure 2 It is the calculated temperature field.

[0018] Figure 3 The range of auxiliary heat sources is determined based on the calculated temperature field.

[0019] Figure 4 This is a comparison of the displacement along the thickness direction after calculation with and without an auxiliary heat source.

[0020] Figure 5 It is the temperature cycle curve of the stress stability zone near the weld.

[0021] Figure 6 This is a three-dimensional schematic diagram of a welding device with an auxiliary heat source.

[0022] Figure 7 This is a two-dimensional schematic diagram of a welding device with an auxiliary heat source. Detailed Implementation

[0023] The present invention will now be described in further detail with reference to the accompanying drawings.

[0024] A method for controlling welding deformation using an auxiliary heat source includes the following steps:

[0025] The first step is to simulate the welding process, including the temperature field and stress-strain field. This is done using a simultaneous coupling method, calculating both the temperature field and the stress-strain field at the same time. The steps for simulating the welding process are as follows:

[0026] 1. Geometric Model Establishment and Mesh Generation: The dimensions of the geometric model are determined based on the actual dimensions of the welded structure. The mesh generation adopts a transitional meshing approach, with a denser mesh near the weld and a sparser mesh further away. The mesh generation is shown in the attached figure. Figure 1 As shown.

[0027] 2. Define material properties and element type: Define performance parameters (including thermal expansion, thermal conductivity, yield strength, Young's modulus, specific heat, density, Poisson's ratio, etc.) based on the actual welding material. The element used is the No. 7 eight-node hexahedral element for thermal / structural analysis.

[0028] 3. Define initial conditions: The initial conditions are the initial temperatures of each node in the geometric model, which are determined by the actual welding process.

[0029] 4. Define boundary conditions: First, displacement constraints were applied to the geometric model, then surface convection conditions were applied to the geometric model, and the ambient temperature was defined.

[0030] 5. Determining the heat source: The heat source model commonly used in this embodiment for welding is the double-ellipsoidal heat source model. The model consists of two double ellipsoids, one in front and one behind. The heat flux distribution expressions for the two semi-ellipsoids are as follows:

[0031]

[0032]

[0033] Q w For heat input power, f f f r are the energy distribution coefficients of the front and rear hemispheres of the double ellipsoidal heat source model, respectively, and f f +f r =2; a f a r b and c are the shape parameters of the heat source, respectively.

[0034] 6. Load step setting: Two load steps are set: one is the load step during the heat source action, and the other is the load step during cooling to room temperature. The action time is 50,000 seconds, and it will automatically end when the temperature reaches room temperature.

[0035] 7. Submit the thermal / structural analysis calculation; the calculated temperature field results are shown in the attached figure. Figure 2 As shown.

[0036] The heat-affected zone (HAZ) range of the welding process was obtained from the above steps. Then, an auxiliary heat source was applied to the HAZ range, as shown in the attached figure. Figure 3 As shown. The addition of an auxiliary heat source is simply a modification to the steps described above; the specific modifications are as follows:

[0037] a. Change and add boundary conditions: Add two unit surface flow conditions in step 5 above, select the area affected by the auxiliary heat source and the area without the auxiliary heat source respectively, and set different ambient temperatures. The ambient temperature of the area affected by the auxiliary heat source should be higher than the preheating temperature, and the ambient temperature of the area without the auxiliary heat source should be room temperature.

[0038] b. Adding and modifying load steps: A load step with an auxiliary heat source as the load was added, and the duration was set to 5000s; an auxiliary heat source was added to the double ellipsoidal heat source load, and the duration remained unchanged.

[0039] c. The temperature field and stress-strain field with the auxiliary heat source were calculated. The displacement results along the plate thickness direction of the centerline perpendicular to the weld direction of the geometric models with and without the auxiliary heat source were compared. The results are shown in the appendix. Figure 4 As shown in the figure, the angular deformation of the calculation model is significantly reduced after adding an auxiliary heat source, decreasing by approximately 33%. Temperature cycle curves of points near the weld center of the two models are also compared, and the results are attached. Figure 5 As shown in the figure, the temperature gradient of the computational model with the auxiliary heat source is significantly smaller than that of the computational model without the auxiliary heat source, and the temperature gradient of the computational model with the auxiliary heat source is also significantly smaller. 8 / 5 The temperature was significantly lower than that of the model without an auxiliary heat source, which significantly reduced the post-weld cooling rate and had a significant impact on suppressing cold cracking.

[0040] As attached Figure 6 As shown, the welding process includes: 1) a welding butt plate with a thickness between 1-100mm; 2) the welding torch used for welding, such as tungsten inert gas welding, shielded metal arc welding, or submerged arc welding, which is used on the front side of the workpiece; and 3) an auxiliary heat source located on the back side of the workpiece, at the centerline of the weld, with the flame nozzle at an angle of 0-90° to the plate. The auxiliary heat source and the welding torch on the front side of the workpiece are positioned back-to-back along the welding direction, with the auxiliary heat source positioned 0-100mm in front of the welding torch. The specific position depends on the distance the welding heat source can radiate to the plate under actual welding conditions. The vertical distance and power of the auxiliary heat source from the workpiece are determined by the range of the heat-affected zone calculated from the simulation. After obtaining the calculation results, the assembled and fixed welding plates are preheated locally with the auxiliary heat source. The preheating temperature is determined by the metallurgical and mechanical properties of the material itself. After the auxiliary heat source has been in effect for a period of time, the surface temperature of the workpiece is measured using a contact thermometer. Once the preheating temperature is reached, welding begins. After welding, the deformation of the welded structure is measured using a ruler.

[0041] Example: The materials to be welded are NM600 steel plates for butt welding, with plate dimensions of 250×300×5mm. A finite element model of the butt plate with dimensions of 250×300×5mm is established. The material properties of NM600 steel, such as thermal expansion, thermal conductivity, yield strength, Young's modulus, specific heat, density, and Poisson's ratio, are defined. The element used is the No. 7 eight-node hexahedral element for thermal / structural analysis. The initial temperature is defined as 20℃. Three-point displacement constraints are applied to the model, and convection is applied to the model surface with a convection coefficient of 3.3×10⁻⁶. -5The ambient temperature was set to 20 degrees Celsius. A double ellipsoidal heat source model was used with parameters ar=3, af=5, b=2.5, c=5, and a welding speed of 4.8 mm / s. A load step during the heat source action was set with an action time of 62 s, and a load step during the cooling process was set with an action time of 50000 s. The thermal / structural analysis was submitted to obtain the temperature field results. Two element-plane flow conditions were added, selecting the auxiliary heat source's action range and the non-action range respectively, and setting the ambient temperatures to 400℃ and 20℃ respectively. A load step with the auxiliary heat source as the load was added, with an action time of 5000 s. The double ellipsoidal heat source load was added with an auxiliary heat source, and the action time remained unchanged. The displacement along the thickness direction after welding was compared between the two models along the direction perpendicular to the weld. The results showed that the angular deformation of the model with the auxiliary heat source was reduced by about 25%, indicating that the auxiliary heat source has a significant effect on reducing angular deformation. Using gas metal arc welding (GMAW), the shielding gas consisted of 80% argon and 20% carbon dioxide. The welding current was 165A, the arc voltage was 15-17V, the angle between the welding torch and the weld centerline was 30°, the welding speed was 4.5mm / s, the auxiliary heat source was 100mm long, the distance between the flame nozzle and the weld plate was 20mm, and the moving speed was 4.5mm / s. After the weld cooled, the measured angular deformation matched the calculated results and was significantly reduced compared to the butt joint angular deformation of plates without an auxiliary heat source.

[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method of controlling welding distortion with the aid of a heat source, characterized by: It comprises the following steps: obtaining the accurate shape and size of a workpiece through three-dimensional scanning, establishing a three-dimensional geometric model with the same shape and size, and performing mesh division on the geometric model, and importing the mesh model after the division into a general finite element software; Defining the initial temperature of the welding process and the ambient temperature, defining the weld and the welding path according to the actual welding condition, selecting an existing heat source model to calculate the temperature field, selecting the peak temperature range from the melting point temperature to 100 DEG C as the auxiliary heat source application range according to the temperature field calculation result, and determining the distance and power of the auxiliary heat source in the vertical direction from the welding plate by the range of the heat affected zone obtained by simulation calculation; The materials to be welded are assembled and fixed, the auxiliary heat source is heated in the auxiliary heat source application range before the welding heat source, and when the temperature of the workpiece in the heating range reaches the specified preheating temperature, the assembled welding materials can be welded; The general finite element software adopts MSC.MARC, Abaqus or ANSYS; The auxiliary heat source selects a flame spray gun to follow the welding gun for heating.

Images