A method for controlling defects in electron beam welding of a girth weld

Abstract

The application provides a kind of annular weld electron beam welding defect control method, including welding before using large defocus electron beam to carry out welding before cleaning near weld, then using large defocus large beam current to carry out welding before surface preheating, welding before small beam current intermittent welding pre-fixing, after official welding, the traditional beam current attenuation is changed into the beam current attenuation value modification beam current while welding focusing current is modified to linear transition focusing current. Make full use of electron beam to carry out welding before cleaning, welding before preheating, welding after modification, without reprogramming after each process, affect welding efficiency. In addition, the smooth transition of electron beam welding before cleaning and welding after modification can effectively reduce the common defects in the welding process, such as: porosity, crack and arc collection defects, so as to maximize the welding quality, and has great application value in actual production.

Description

Technical Field

[0001] This invention belongs to the field of electron beam welding technology, and particularly relates to a method for controlling defects in electron beam welding of circumferential welds. Background Technology

[0002] Vacuum electron beam welding, because the workpiece is placed in a vacuum environment during the welding process, eliminates the need for welding protection. Therefore, porosity primarily arises from oil, moisture, and oxide films on the workpiece surface during welding. Furthermore, sudden changes in heat input during welding can cause pits or weld beads, defects that are prone to occur during the arc initiation and termination stages. In addition, traditional preheating and post-weld heat treatment are limited by the vacuuming and gas inlet time constraints of electron beam welding, making it impossible to perform pre- and post-weld heat treatments on the workpiece. When welding materials with a high hardening tendency, cracking often leads to the scrapping of the workpiece. In summary, current electron beam welding does not fully utilize the heating characteristics of electron beams to control defects in the electron beam welding process of circumferential welds. Summary of the Invention

[0003] The purpose of this invention is to provide a method for controlling defects in electron beam welding of circumferential welds. This method aims to fully utilize the high heat characteristic of electron beams, and achieve pre-weld cleaning, pre-weld preheating, and post-weld heat preservation by simply changing the beam current and focusing current. It also strictly controls the rate of parameter changes between each process, and completes the entire process from pre-weld cleaning to post-weld heat preservation in one procedure, thereby improving welding efficiency and weld quality.

[0004] The technical solution to achieve the purpose of this invention is as follows:

[0005] A method for controlling defects in electron beam welding of circumferential welds, wherein pre-weld cleaning, pre-weld preheating, pre-weld pre-fixing, formal welding, finishing welding, and post-weld heat preservation are all completed using an electron beam; specifically, it includes the following steps:

[0006] Pre-welding cleaning stage: The area around the welding position is cleaned using a small beam current, a large focusing current, and defocusing; the focusing current in this stage is F1, and the beam current is I1.

[0007] Formal welding stage: Preheating of the welding position is performed using a small beam current, a small focusing current, and a defocusing mode; the focusing current in this stage is F2, and the beam current is I2.

[0008] Finishing and welding stage: A small current beam, a marked welding focusing current, and an electron beam are focused on the workpiece surface to perform spot welding and fixation at the position to be welded; the focusing current in this stage is F3 = F H The beam current is I3;

[0009] Formal welding stage: Continuous welding is performed by focusing the electron beam on the workpiece surface using a pre-set beam current and welding focus current; the focus current in this stage is F. H The beam current is I H ;

[0010] Modification welding stage: The workpiece to be welded is modified and welded using a small beam current, a large focusing current, and an upper defocusing mode; the focusing current in this stage is F5, and the beam current is I5.

[0011] Post-weld heat preservation stage: The workpiece to be welded is heat preserved by using a small beam current, a small focusing current, and a defocusing mode; the focusing current in this stage is F6 and the beam current is I6.

[0012] Where F1 > F5 > F H >F2, F1>F5>F H >F6; I H >I2>I5>I3>I1; I H >I6>I5>I3>I1.

[0013] The significant advantages of this invention compared to existing technologies are:

[0014] Electron beam pre-welding cleaning removes surface oxide films, moisture, and oil. Preheating before electron beam welding and post-weld heat preservation reduce the generation of crack defects. Dynamic changes in beam parameters between processes, without shutting down the beam, minimize the time the workpiece spends cooling, maximizing heat utilization and saving energy. Strict control of the parameter change rate between processes effectively reduces pits and weld beads caused by sudden parameter changes. In summary, this invention reduces defects in the electron beam welding of circumferential welds. Attached Figure Description

[0015] Figure 1 It is a graph showing the rate of change of parameters throughout the entire process.

[0016] Figure 2 This is a schematic diagram of electron beam cleaning before welding.

[0017] Figure 3 This is a schematic diagram of electron beam preheating before welding.

[0018] Figure 4 This is a schematic diagram of electron beam pre-welding.

[0019] Figure 5 This is a schematic diagram of electron beam welding.

[0020] Figure 6 This is a schematic diagram of the welding process.

[0021] Figure 7 This is a schematic diagram of electron beam heat preservation after welding.

[0022] Figure 8 The surface of the weld seam of a 5mm thick molybdenum alloy cylindrical section obtained by welding using this method.

[0023] In the figure: 1 is the parameter of the electron beam cleaning stage before welding, 2 is the parameter of the electron beam preheating stage, 3 is the parameter of the electron beam pre-welding stage, 4 is the parameter of the electron beam welding stage, 5 is the parameter of the electron beam modification welding stage, 6 is the parameter of the post-weld heat preservation stage, 7 is the workpiece, 8 is the position to be welded, 9 is the electron beam, 10 is the electron beam cleaning area, 11 is the preheating area before welding, 12 is the pre-welding point, 13 is the weld, 14 is the modified weld, and 15 is the post-weld heat preservation area. Detailed Implementation

[0024] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0025] The present invention provides a method for controlling defects in electron beam welding of circumferential welds, comprising the following steps:

[0026] Step 1, as follows Figure 1 As shown in stage 1, the first step is to perform electron beam cleaning before welding. Before welding, a small beam current and upper decoking method are used to clean the area near the welding position. This method can effectively remove oil and water and oxide film from the surface of the weldment and reduce the porosity in the weld.

[0027] The specific parameters are: focusing current F1 is F H +100 (mA), beam current I1 = I H / 6(mA), a schematic diagram of the electron beam's effective range and cleaning area is shown below. Figure 2 As shown, 9 is the electron beam, 7 is the workpiece, 8 is the position to be welded, and 10 is the electron beam cleaning area. Figure 1 The square marking represents the actual focusing current, and the circle represents the actual beam current. Where F... H This represents the focused current during the actual welding process (dashed line in the diagram). H This is the beam current used during the actual welding process.

[0028] Step 2: Preheat the workpiece before welding. For materials prone to cracking defects during welding, after electron beam pre-welding cleaning, a low beam current and downward defocusing mode can be used to preheat the area to be welded.

[0029] The specific parameters are: focusing current F2 is F H -70 (mA), beam current I2 = I H / 2(mA), the electron beam changes from upper defocus to lower defocus, which can fully utilize the heat input of the electron beam for preheating before welding. The schematic diagram of the electron beam's effective range and preheating area during electron beam preheating is shown in the figure. Figure 3 As shown, 11 is the preheating zone before welding.

[0030] Step 3, as follows Figure 1 In the third stage, electron beam spot welding is used to pre-fix the welding position to prevent welding defects caused by thermal deformation during the welding process. The beam current is reduced to the pre-welding stage value, and the focusing current increases to focus the electron beam on the workpiece surface. Specific parameters are: focusing current F3 is F... H (mA), beam current I3=I H / 3(mA), pre-welding diagram as shown Figure 4 As shown, 12 is the pre-welding point and 13 is the weld.

[0031] Step 4, as follows Figure 1 In the fourth stage, the workpieces to be welded are formally welded. The welding mode is changed from spot welding or intermittent welding to continuous welding. The specific parameters are: focusing current is F. H (mA), beam I H (mA), the formal welding diagram is as follows Figure 5 As shown, the dashed line represents the standard focusing current used during the welding stage.

[0032] Step 5, as follows Figure 1 In the fifth stage, the workpiece is modified and welded. The focusing current is increased, and the electron beam changes from a surface-focused state to an upper-defocused state. The specific parameters are: focusing current F5 is F H +50 (mA), beam current I5 = 0.4·I H (mA), the modified welding diagram is as follows Figure 6 As shown, 14 is the modified weld.

[0033] Step 6, as follows Figure 1 In stage 6, the workpiece is held at a constant temperature after welding. The focusing current is reduced, the electron beam becomes defocused, and the beam current rises to the holding current. Specific parameters are: focusing current F6 is F... H -70 (mA), beam current I6 = 0.5·I H (mA), the modified welding diagram is as follows Figure 7 As shown, 15 represents the area requiring post-weld insulation.

[0034] Finally, the focusing parameters remain unchanged, and the beam current gradually decreases to 0, completing the welding process.

[0035] Example 1

[0036] Taking electron beam welding of a 5mm thick molybdenum alloy cylindrical section as an example, firstly... Figure 1 As shown, the molybdenum alloy cylindrical section was subjected to a bearing. The working distance was measured to be 300 mm. At this distance, the focusing current of the surface focal point was 1420 mA, and the formal welding beam current was 30 mA.

[0037] Step 1, as follows Figure 1As shown in stage 1, the first step is pre-welding electron beam cleaning, with specific parameters as follows: focusing current 1520 mA, beam current 5 mA. A schematic diagram of the electron beam's effective range and cleaning area is shown below. Figure 2 As shown, 10 represents the electron beam cleaning area.

[0038] Step 2: Preheat the workpiece before welding. Specific parameters are: focusing current 1350 mA, beam current 15 mA, and the electron beam changes from upper defocus to lower defocus. This fully utilizes the heat input from the electron beam for preheating. A schematic diagram of the electron beam's effective range and preheating area during preheating is shown below. Figure 3 As shown, 11 is the preheating zone before welding.

[0039] Step 3, as follows Figure 1 In the third stage, the workpiece is fixed by spot welding or intermittent welding. Then, the beam current is reduced to the pre-welding stage value, and the focusing current is increased to focus the electron beam on the workpiece surface. The specific parameters are: focusing current of 1420 mA and beam current of 10 mA. The pre-welding schematic diagram is shown below. Figure 4 As shown, 12 is a pre-soldering point.

[0040] Step 4, as follows Figure 1 In the fourth stage, the workpieces to be welded are formally welded. The welding mode is changed from spot welding or intermittent welding to continuous welding. The specific parameters are: focusing current of 1420 mA and beam current of 30 mA. The formal welding diagram is shown below. Figure 5 As shown, 13 is the weld seam.

[0041] Step 5, as follows Figure 1 In the fifth stage, the workpiece is modified and welded. The focusing current increases, and the electron beam changes from a surface-focused state to an upper-defocused state. The specific parameters are: focusing current of 1470 mA and beam current of 12 mA. The modification and welding schematic diagram is shown below. Figure 6 As shown, 14 is the modified weld.

[0042] Step 6, as follows Figure 1 In stage 6, the workpiece is held at a constant temperature after welding. The focusing current is reduced, the electron beam becomes defocused, and the beam current rises to the holding current. Specific parameters are: focusing current 1350 mA, beam current 15 mA. A schematic diagram of the finishing weld is shown below. Figure 7 As shown, 15 represents the post-weld insulation area.

[0043] Finally, with the focusing parameters remaining constant, the beam current gradually decreases to zero, completing the welding process. This method yields welds with good surface finish, such as... Figure 8 As shown, there are no arc termination defects. X-ray inspection revealed that there are no pores inside the weld and no cracking after welding.

Claims

1. A method for controlling defects in electron beam welding of circumferential welds, characterized in that, Pre-welding cleaning, pre-welding preheating, pre-welding pre-fixing, formal welding, finishing welding, and post-weld heat preservation are all completed using an electron beam; specifically, the following steps are included: Pre-welding cleaning stage: The area around the welding position is cleaned using a small beam current, a large focusing current, and defocusing; the focusing current in this stage is F1, and the beam current is I1. Preheating stage: Preheating of the position to be welded is performed using a small beam current, a small focusing current, and a defocusing mode; the focusing current in this stage is F2, and the beam current is I2. Spot welding stage: small beam current, focus current marked welding, electron beam focusing on the workpiece surface to fix the position to be welded; the focus current of this stage is F3=F H , beam current is I3; Formal welding stage: adopt the set mark beam current, mark welding focus current, electron beam focus on the workpiece surface to carry on the continuous welding; the focus current of this stage is F H , the beam current is I H ; Modification welding stage: The workpiece to be welded is modified and welded using a small beam current, a large focusing current, and an upper defocusing mode; the focusing current in this stage is F5, and the beam current is I5. Post-weld heat preservation stage: The workpiece to be welded is heat preserved by using a small beam current, a small focusing current, and a defocusing mode; the focusing current in this stage is F6 and the beam current is I6. wherein F1>F5>F H F2, F1>F5>F H F6; I H I2>I5>I3>I1; I H I6>I5>I3>I1.

2. The method for controlling defects in electron beam welding of circumferential welds according to claim 1, characterized in that, F2 = F6.

3. The method for controlling defects in electron beam welding of circumferential welds according to claim 1, characterized in that, I2 = I6.

4. The method for controlling defects in electron beam welding of circumferential welds according to claim 1, characterized in that, F1 = F H + 100, I1 = I H / 6.

5. The method for controlling defects in electron beam welding of circumferential welds according to claim 1, characterized in that, F2=F H -70,I2=I H / 2。 6. The method for controlling defects in electron beam welding of circumferential welds according to claim 1, characterized in that, I3=I H / 3。 7. The method for controlling defects in electron beam welding of circumferential welds according to claim 1, characterized in that, F5=F H +50,I5=0.4·I H 。 8. The method for controlling defects in electron beam welding of circumferential welds according to claim 1, characterized in that, F6=F H -70,I6=0.5·I H 。

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