A welding method for reducing weld cracking of a titanium alloy welding electrode

Abstract

The application discloses a welding method for reducing weld cracks of a titanium alloy welding electrode, and specifically realizes the method by the following steps: welding a stack electrode into a first weld seam through a conventional method, re-heating the first weld seam, rotating the stack electrode and forming other weld seams in a diagonal manner, and re-heating each weld seam after being formed. By using the method, welding thermal stress can be fully released in the welding process, and the weld seam is prevented from cracking in the cooling process, so that the purpose of not needing to return to the furnace for repair welding is achieved.

Description

Technical Field

[0001] This invention relates to the field of metal welding technology, and more specifically to a welding method for reducing weld cracks in titanium alloy welding electrodes. Background Technology

[0002] Titanium and titanium alloys possess excellent properties such as low density, high specific strength, and good corrosion resistance, making them widely used in aerospace, automotive, chemical, and medical industries. The smelting of titanium ingots is the first step in producing high-quality titanium products. The smelting process generally involves three steps: electrode pressing, electrode welding, and electrode melting. The quality of the weld seam in the electrode welding stage plays a crucial role in the smooth progress of the subsequent electrode melting process.

[0003] Electrode assembly welding is the process of arranging pressed, disc-shaped electrode blocks according to specific rules and welding them together in a vacuum plasma welding box to form a columnar welding electrode of a certain length. Due to the reactive chemical properties of titanium alloys and the need to prevent high-density inclusions, titanium alloy welding requires an argon-protected atmosphere. The plasma generated by a water-cooled copper welding torch melts the pressed electrodes, forming welds between the electrode blocks to connect them into a whole. The weld not only serves as a tensile connecting element during electrode assembly but also acts as a conductive path during vacuum arc remelting. When the weld cracks, the conductivity and mechanical strength of the welding electrode decrease, potentially leading to fragmentation or breakage during subsequent melting. This not only increases the risk of metallurgical defects during titanium alloy melting but also poses a significant safety risk of accidents during the melting process. Current technology typically addresses the cracking problem caused by thermal stress during the cooling process by re-welding in the furnace. The remelt welding method involves removing the welding electrode from the furnace after 120 minutes of cooling to inspect the weld quality, marking any cracks, reinstalling the electrode in the welding box, evacuating the welding box, purging with argon gas, welding at the marked areas, and then cooling and removing it from the furnace. Remelt welding has several disadvantages:

[0004] The repair welding process is lengthy, and the weld may continue to crack during the repair welding process, which may require multiple re-weldings, resulting in more labor hours, argon gas consumption, etc., which increases production costs and reduces production efficiency.

[0005] The repair welding process requires manual operation of a welding gun to repair the cracked area using plasma arc lighting. This process is very easy to miss the cracked area during the remelting process, which may lead to safety risks in the melting process.

[0006] The process of re-welding requires taking the electrodes out of the furnace and loading them back into the furnace, which prolongs the time the welding electrodes are stored in the air. This causes the welding electrodes to absorb more moisture, affecting the oxygen content of the final product. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the purpose of this invention is to provide a welding method to reduce weld cracks in titanium alloy welding electrodes, which can reduce the need for remelting.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A welding method for reducing weld cracks in titanium alloy welding electrodes, characterized by comprising the following steps:

[0010] Step 1) Arrange and stack multiple electrode blocks on the rollers of the vacuum plasma welding box as required to form a stacked electrode. The total length of the stacked electrode is 1000-7000mm; and apply axial pressure to the end face.

[0011] Specifically, the pressed electrode is a disc-shaped electrode pressed by a hydraulic press. The electrode diameter applicable to this invention is Φ300mm-Φ900mm, and the total length of the multi-layer electrode blocks after stacking is 1000mm-7000mm. The axial pressure applied during stacking is used to control the gap between the electrode blocks, and an appropriate pressure is selected according to the gap size.

[0012] Step 2) Use the trolley attached to the vacuum plasma welding box to send the stacked electrode from Step 1 into the welding box, and adjust the position of the stacked electrode head to be directly below the welding torch, and define this as the welding zero point and angle zero point; then start to evacuate to ≤10Pa, and after the vacuum is in place, perform leak detection, requiring a leak rate ≤1Pa / min; when all vacuum conditions are met, fill the welding box with argon gas, and control the argon gas pressure at 30000-60000Pa;

[0013] Specifically, titanium, as a reactive metal, readily reacts with elements such as O and N in the air. Therefore, titanium welding must be performed under argon protection. Evacuating the vacuum plasma welding box and specifying a certain leakage rate can prevent electrode oxidation during the welding process. The vacuum plasma welding box needs to be in an argon atmosphere at a certain pressure, and the axial position and angle of the welding electrode must be accurately positioned during the welding process to ensure that the welding is performed according to the set position and angle.

[0014] Step 3) Set the standard welding parameters, specifically the welding current of 200-700A, welding voltage of 40-90V, argon flow rate of 5-30L / min, welding speed of 30-100mm / min, turn on the automatic welding mode, and start welding the first weld. When welding to the bottom of the electrode, turn off the welding and raise the welding torch.

[0015] The welding parameters in this step are based on conventional welding methods derived from equipment and experience. The density of the electrode weld is greater than that of the electrode block. During the solidification process of the weld pool, the pressed electrode transforms into a solid state, and the increased density leads to weld shrinkage. Therefore, the welding speed should not be too high, as this can easily result in insufficient heat concentration, inadequate weld depth, and the weld remaining only on the electrode surface, resulting in insufficient weld strength. Conversely, the welding speed should not be too low, as this will lead to concentrated heat during the welding process, a deeper weld pool, and more severe shrinkage during solidification, causing concentrated thermal stress in the weld, which can lead to electrode bending and weld cracking. Based on the above welding parameters, the weld should be straight, with a weld depth ≥30mm and a weld width ≥30mm. The welding process, depending on the electrode length, requires 10-60 minutes for a single weld pass.

[0016] Step 4) Move the stacked electrode to the welding zero point, reset the welding parameters, and use a welding current and welding voltage lower than those used for the first weld, as well as a welding speed faster than that used for the first weld. Specifically, adjust the welding current, voltage, argon flow rate and welding speed according to the state of the weld pool, so that the weld pool is about to form but has not yet formed. Restart the automatic welding mode, heat the weld at the position of the first weld, and then close the welding program after welding to the bottom of the electrode. Raise the welding torch and move the stacked electrode to the welding zero point.

[0017] This step involves using lower current and voltage (lower welding input power) and a faster welding speed after a conventional weld has been completed. This avoids melting the original weld and reheating it. When the electrode length is long, the temperature difference between the welding zero point and the welding end point is significant. Uneven rates of thermal stress release during cooling can lead to weld cracking. This step uses plasma to reheat the weld, ensuring a more uniform temperature across the entire weld and guaranteeing a consistent rate of thermal stress release during cooling. This is equivalent to performing stress-relieving annealing on the entire weld, reducing the likelihood of cracking.

[0018] Step 5): Rotate the stacked electrode to 180° of the zero angle, repeat steps 3) and 4); rotate the stacked electrode again to 270° of the zero angle, repeat steps 3) and 4); rotate the stacked electrode again to 90° of the zero angle, repeat steps 3) and 4); rotate the stacked electrode again to 315° of the zero angle, repeat steps 3) and 4); rotate the stacked electrode again to 135° of the zero angle, repeat steps 3) and 4); rotate the stacked electrode again to 45° of the zero angle, repeat steps 3) and 4); rotate the stacked electrode again to 225° of the zero angle, repeat steps 3) and 4); then rotate the stacked electrode back to the zero angle and move the stacked electrode to the welding zero point;

[0019] This step involves rotating the electrode by a certain angle and then repeating steps 3 and 4. Welding is performed at specific angles to ensure symmetrical welding; that is, after welding one weld, the next weld is welded at 180°. When a weld is completed, the shrinkage of the weld causes the electrode on that side to bend inward under compressive stress, while the electrode on the 180° symmetrical side experiences tensile stress, ultimately causing the electrode to bend into an arc shape. Welding one weld and then the next on the 180° symmetrical side corrects the electrode bending caused by the previous weld, making the electrode straighter. Furthermore, distributing the eight welds evenly at 45° intervals on the electrode allows for a more uniform release of the stress from weld shrinkage, resulting in better electrode straightness and preventing stress concentration caused by localized weld concentrations that could lead to cracking.

[0020] Step 6) Reset the welding parameters, using a welding current and welding voltage lower than those used in Step 4), and a faster welding speed than in Step 4). Specifically, adjust the welding current, voltage, argon flow rate, and welding speed according to the state of the molten pool to achieve the best result of hot purging the weld without melting it. Restart the welding program at the welding zero point, so that the plasma welding gun performs hot purging at the position of the first weld until the bottom of the electrode, and then move the stacked electrode to the welding zero point.

[0021] Step 6 uses lower welding current and voltage and a faster welding speed compared to step 4, with a similar purpose. In step 5, all eight weld seams have been completed, but the time from welding the first weld seam to the completion of the eighth weld seam has lasted 200-480 minutes. The cooling time of the first weld seam is 200-480 minutes longer than that of the eighth weld seam, resulting in a significant difference in the degree of welding thermal stress release. This step uses lower-power plasma to sequentially purge and heat the eight weld seams, raising their temperature and allowing for more uniform cooling. This is equivalent to performing stress-relieving annealing at a lower temperature, reducing weld cracking.

[0022] Step 7) Rotate the stacked electrode sequentially to 45°, 90°, 135°, 180°, 225°, 270°, and 315° from the zero angle point, then repeat step 6); close the welding program, raise the welding torch, and move the stacked electrode to the welding zero point.

[0023] Step 8) Evacuate the welding box to 10-100Pa, then turn off the vacuum pump unit. After at least 120 minutes, break the vacuum in the welding box, remove the electrodes, and check the weld quality of the electrodes.

[0024] This step involves the vacuum cooling process of the welding electrode. The vacuum plasma welding chamber is evacuated after welding to reduce the cooling rate of the welding electrode. When the atmosphere inside the welding chamber is 30,000~60,000 Pa (the working atmosphere), the argon gas medium causes a large heat dissipation capacity of the electrode, resulting in an excessively high cooling rate of the weld and rapid release of thermal stress, which can lead to weld cracking. This step evacuates the argon gas inside the welding chamber to 10-100 Pa, reducing the argon gas medium and thus helping to lower the cooling rate of the weld and reduce the likelihood of cracking. The cooling time in this step is controlled to be more than 120 minutes, allowing sufficient time for the weld to slowly release stress and prevent electrode cracking.

[0025] Preferably, in step 1) above, after all the electrode blocks are stacked, axial pressure is applied to the end face so that the gap between two adjacent electrode blocks is controlled at 1-5mm.

[0026] Preferably, in step 4) above, the welding current is 100-600A, the welding voltage is 30-80V, the argon flow rate is 5-30L / min, and the welding speed is 60-100mm / min.

[0027] Preferably, in step 6) above, the welding current is 100-500A, the welding voltage is 30-70V, the argon flow rate is 5-30L / min, and the welding speed is 80-120mm / min.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The method of this invention can fully release welding thermal stress during the welding process, avoid cracking of the weld during cooling, and ultimately achieve the goal of not needing to remelt for repair welding. Attached Figure Description

[0030] Figure 1 This is a photograph of the welding quality of Comparative Example 1 of the present invention;

[0031] Figure 2 This is a photograph of the welding quality of Comparative Example 2 of the present invention;

[0032] Figure 3 This is a photograph of the welding quality of Embodiment 1 of the present invention. Detailed Implementation

[0033] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention. Specific embodiments are provided below to describe the method of this application. Other preparation parameters not mentioned in each embodiment are consistent in all embodiments.

[0034] It should be understood that these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this invention. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0035] The pressed electrode is a regular electrode block made by pressing a mixture of sponge titanium and intermediate alloy using a hydraulic press. Depending on the pressure of the press, the density of the electrode block ranges from 3.0 to 3.7 g / cm³. 3 Between. The welding process of the electrode blocks relies on high-temperature plasma to melt and then solidify a portion of the electrode surface to form a weld, thereby connecting the electrode blocks. Although the sponge titanium and intermediate alloy have been pressed by a hydraulic press, their density is still similar to that of solidified titanium alloy (4.5 g / cm³). 3 In comparison, a significant density difference still exists, and the strength of the solidified electrode is significantly higher than that of the pressed electrode. This difference in density and strength makes the weld prone to cracking during the release of thermal stress. Furthermore, the gap between the stacked electrode blocks cannot be too small or too large. During the solidification of the weld pool, the increased density causes weld shrinkage. If the gap is too small, the shrinkage distance is insufficient, leading to weld cracks. Conversely, if the gap is too large, the molten metal in the weld pool will flow along the gap between the electrode blocks, resulting in an incomplete weld pool and a weak weld. This invention, through multiple experiments, has verified that a gap of 1-5 mm can meet the requirements for weld shrinkage and a full molten pool.

[0036] Comparative Example 1

[0037] Step 1) Stack the Φ420×4400mm electrodes of TC4 on the rollers of the vacuum plasma welding box, apply axial compressive stress, and control the electrode gap to be 1-5mm.

[0038] Step 2) Using the trolley attached to the vacuum plasma welding box, drive the stacked electrode blocks into the box, adjust the electrode head position to be directly below the welding torch, and set this point as the welding zero point and angle zero point. Then, begin evacuating to ≤10Pa. After the vacuum is achieved, perform leak testing, requiring a leak rate ≤1Pa / min. Once all vacuum conditions are met, purge the welding box with argon gas, controlling the argon gas pressure at 30000-60000Pa.

[0039] Step 3) Set the welding parameters: welding current 200-700A, welding voltage 40-90V, argon flow rate 5-30L / min, welding speed 30-100mm / min. Then start the welding program and activate the automatic welding mode to begin welding the first weld. Once the electrode is reached, close the welding program and raise the welding torch.

[0040] Step 4) Rotate the electrode to 180° of the zero angle point and repeat Step 3; rotate the electrode to 270° of the zero angle point again and repeat Step 3; rotate the electrode to 90° of the zero angle point again and repeat Step 3; rotate the electrode to 315° of the zero angle point again and repeat Step 3; rotate the electrode to 135° of the zero angle point again and repeat Step 3; rotate the electrode to 45° of the zero angle point again and repeat Step 3; rotate the electrode to 225° of the zero angle point again and repeat Step 3; rotate the welding electrode to the welding angle zero point and move the carriage to the welding zero point;

[0041] Step 5) Turn on the vacuum pump unit of the vacuum plasma welding box, evacuate the vacuum inside the welding box to 10-100Pa, and then turn off the vacuum pump unit. After at least 120 minutes, break the vacuum in the welding box, drive the electrode out of the trolley, and check the weld quality of the welding electrode.

[0042] The welding quality of this comparative example is as follows: Figure 1 As shown, the electrode is severely bent, and the weld is noticeably cracked.

[0043] Comparative Example 2

[0044] Step 1) Stack the Φ420×4400mm electrodes of TC4 on the rollers of the vacuum plasma welding box, apply axial compressive stress, and control the electrode gap to be 1-5mm.

[0045] Step 2) Using the trolley attached to the vacuum plasma welding box, drive the stacked electrode blocks into the box, adjust the electrode head position to be directly below the welding torch, and set this point as the welding zero point and angle zero point. Then, begin evacuating to ≤10Pa. After the vacuum is achieved, perform leak testing, requiring a leak rate ≤1Pa / min. Once all vacuum conditions are met, purge the welding box with argon gas, controlling the argon gas pressure at 30000-60000Pa.

[0046] Step 3) Set the welding parameters: welding current 200-700A, welding voltage 40-90V, argon flow rate 5-30L / min, welding speed 30-100mm / min. Then start the welding program and activate the automatic welding mode to begin welding the first weld. Once the electrode is reached, close the welding program and raise the welding torch.

[0047] Step 4) Move the carriage to the welding zero point, reset the welding parameters: welding current 100-600A, welding voltage 30-80V, argon flow rate 5-30L / min, welding speed 60-100mm / min. Then start the welding program at the welding zero point. Restart the automatic welding mode until welding reaches the bottom of the electrode, then close the welding program and raise the welding torch. Move the carriage to the welding zero point.

[0048] Step 5) Rotate the electrode to 180° of the zero angle point, and repeat steps 3 and 4; rotate the electrode to 270° of the zero angle point again, and repeat steps 3 and 4; rotate the electrode to 90° of the zero angle point again, and repeat steps 3 and 4; rotate the electrode to 315° of the zero angle point again, and repeat steps 3 and 4; rotate the electrode to 135° of the zero angle point again, and repeat steps 3 and 4; rotate the electrode to 45° of the zero angle point again, and repeat steps 3 and 4; rotate the electrode to 225° of the zero angle point again, and repeat steps 3 and 4; rotate the welding electrode to the welding angle zero point, and move the carriage to the welding zero point.

[0049] Step 6) Turn on the vacuum pump unit of the vacuum plasma welding box, evacuate the vacuum inside the welding box to 10-100Pa, and then turn off the vacuum pump unit. After at least 120 minutes, break the vacuum in the welding box, drive the electrode out of the trolley, and check the weld quality of the welding electrode.

[0050] The difference between Comparative Example 2 and Comparative Example 1 is that only step 4, a stress-relief annealing weld, was added after one weld seam was completed. The welding quality of this comparative example is as follows: Figure 2 As shown, the electrode is not bent, but there are still small cracks in the weld. Example

[0051] Step 1) Stack the Φ420×4400mm electrodes of TC4 on the rollers of the vacuum plasma welding box, apply axial compressive stress, and control the electrode gap to be 1-5mm.

[0052] Step 2) Using the trolley attached to the vacuum plasma welding box, drive the stacked electrode blocks into the box, adjust the electrode head position to be directly below the welding torch, and set this point as the welding zero point and angle zero point. Then, begin evacuating to ≤10Pa. After the vacuum is achieved, perform leak testing, requiring a leak rate ≤1Pa / min. Once all vacuum conditions are met, purge the welding box with argon gas, controlling the argon gas pressure at 30000-60000Pa.

[0053] Step 3) Set the welding parameters: welding current 200-700A, welding voltage 40-90V, argon flow rate 5-30L / min, welding speed 30-100mm / min. Then start the welding program and activate the automatic welding mode to begin welding the first weld. Once the electrode is reached, close the welding program and raise the welding torch.

[0054] Step 4) Move the carriage to the welding zero point, reset the welding parameters: welding current 100-600A, welding voltage 30-80V, argon flow rate 5-30L / min, welding speed 60-100mm / min. Then start the welding program at the welding zero point. Restart the automatic welding mode until welding reaches the bottom of the electrode, then close the welding program and raise the welding torch. Move the carriage to the welding zero point.

[0055] Step 5) Rotate the electrode to 180° of the zero angle point, and repeat steps 3 and 4; rotate the electrode to 270° of the zero angle point again, and repeat steps 3 and 4; rotate the electrode to 90° of the zero angle point again, and repeat steps 3 and 4; rotate the electrode to 315° of the zero angle point again, and repeat steps 3 and 4; rotate the electrode to 135° of the zero angle point again, and repeat steps 3 and 4; rotate the electrode to 45° of the zero angle point again, and repeat steps 3 and 4; rotate the electrode to 225° of the zero angle point again, and repeat steps 3 and 4; rotate the welding electrode to the welding angle zero point, and move the carriage to the welding zero point.

[0056] Step 6) Reset the welding parameters: welding current 100-500A, welding voltage 30-70V, argon flow rate 5-30L / min, welding speed 80-120mm / min. Adjust the welding current, voltage, argon flow rate, and welding speed according to the state of the molten pool. Start the welding program at the welding zero point, allowing the plasma to sweep across the weld seam until it reaches the bottom of the welding electrode. Move the carriage to the welding zero point.

[0057] Step 7) Rotate the electrode sequentially to 45°, 90°, 135°, 180°, 225°, 270°, and 315° from the zero angle point, then repeat step 6. Close the welding program, raise the welding torch, and move the carriage to the zero position.

[0058] Step 8) Turn on the vacuum pump unit of the vacuum plasma welding box, evacuate the vacuum inside the welding box to 10-100Pa, and then turn off the vacuum pump unit. After at least 120 minutes, break the vacuum in the welding box, drive the electrode out of the trolley, and check the weld quality of the welding electrode.

[0059] The difference between Example 1 and Comparative Example 2 is that only step 6, a stress-relief annealing weld, was added after all 8 welds were completed. The welding quality of Example 1 is as follows: Figure 3 As shown. The electrode straightness is good, and the weld is not cracked.

Claims

1. A welding method for reducing weld cracks in titanium alloy welding electrodes, characterized in that, Includes the following steps: Step 1) Arrange and stack multiple electrode blocks on the rollers of the vacuum plasma welding box as required to form stacked electrodes. The total length of the stacked electrodes is 1000-7000mm. Step 2) Welding is performed using a vacuum plasma welding box. The stacked electrode from Step 1) is sent into the welding box and the position of the stacked electrode head is adjusted to be directly below the welding torch. This position is defined as the welding zero point and angle zero point. Vacuum is drawn, and then argon gas is filled into the welding box. The argon gas pressure is controlled at 30,000-60,000 Pa. Step 3) Set the welding parameters: welding current 200-700A, welding voltage 40-90V, argon flow rate 5-30L / min, welding speed 30-100mm / min. Then start the welding program and begin welding the first weld. When the welding reaches the bottom of the electrode, turn off the welding. Step 4) Move the stacked electrode to the welding zero point, and use a welding current and welding voltage lower than those used for the first weld, as well as a welding speed faster than that used for the first weld, to heat the weld again at the position of the first weld. After completion, move the stacked electrode to the welding zero point, where the welding current is 100-600A, the welding voltage is 30-80V, the argon flow rate is 5-30L / min, and the welding speed is 60-100mm / min. Step 5): Rotate the stacked electrode to 180° of the zero angle, repeat steps 3) and 4); rotate the stacked electrode again to 270° of the zero angle, repeat steps 3) and 4); rotate the stacked electrode again to 90° of the zero angle, repeat steps 3) and 4); rotate the stacked electrode again to 315° of the zero angle, repeat steps 3) and 4); rotate the stacked electrode again to 135° of the zero angle, repeat steps 3) and 4); rotate the stacked electrode again to 45° of the zero angle, repeat steps 3) and 4); rotate the stacked electrode again to 225° of the zero angle, repeat steps 3) and 4); then rotate the stacked electrode back to the zero angle and move the stacked electrode to the welding zero point; Step 6) Using a welding current and welding voltage less than those used in Step 4), and a faster welding speed than in Step 4), perform hot purging at the position of the first weld. After completion, move the stacked electrode to the welding zero point. The welding current is 100-500A, the welding voltage is 30-70V, the argon flow rate is 5-30L / min, and the welding speed is 80-120mm / min. Step 7) Rotate the stacked electrode sequentially to 45°, 90°, 135°, 180°, 225°, 270°, and 315° from the zero angle point, then repeat step 6); After completion, move the stacked electrode to the welding zero point; Step 8) Evacuate the welding box to 10-100 Pa, then turn off the vacuum pump unit and remove the electrode from the welding box after it has cooled for a period of time.

2. The welding method for reducing weld cracks in titanium alloy welding electrodes according to claim 1, characterized in that, In step 1) above, after all the electrode blocks are stacked, axial pressure is applied to the end face so that the gap between two adjacent electrode blocks is controlled at 1-5mm.

3. A welding method for reducing weld cracks in titanium alloy welding electrodes according to claim 1 or 2, characterized in that, The cooling time in step 8) above is at least 120 minutes.

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