Welding method for reducing welding seam cracks of titanium alloy welding electrode

Abstract

The invention discloses a welding method for reducing weld cracks of a titanium alloy welding electrode, which specifically comprises the following steps of: conventionally welding a stacked electrode into a first weld through a conventional method, reheating the first weld once, rotating the stacked electrode and forming other welds in a diagonal manner, and reheating once after each welding seam is formed, and the like. By the adoption of the method, welding thermal stress can be fully released in the welding process, a weld joint is prevented from cracking in the cooling process, and finally the purpose that remelting for repair welding is not needed is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of metal welding, and in particular to a welding method for reducing weld cracks of titanium alloy welding electrodes. Background Art

[0002] Titanium and titanium alloys have excellent properties such as low density, high specific strength, and good corrosion resistance. They are widely used in aerospace, automotive, chemical, medical and other industries. The smelting of titanium ingots is the first step in preparing excellent titanium products. The smelting process of titanium ingots generally consists of three steps: electrode pressing, electrode welding, and electrode smelting. The weld quality of electrode welding plays a key role in the smooth progress of the subsequent electrode smelting process.

[0003] Electrode group welding is the process of arranging the pressed pancake-shaped electrode blocks according to corresponding rules, welding them together in a vacuum plasma welding box, and forming a columnar welding electrode with a certain length. Due to the active chemical properties of titanium alloys and the need to prevent high-density inclusions, the welding of titanium alloys requires the use of plasma generated by a water-cooled copper welding gun to melt the pressed electrode as the parent material under an argon protection atmosphere, and forming welds between the electrode blocks to connect the electrode blocks into a whole. The weld not only plays a connecting role in withstanding tension during the electrode block assembly process, but also plays a conductive role as a channel for current during vacuum consumable melting. When the weld cracks, the conductivity and mechanical strength of the welding electrode will decrease, and it may fall off in the subsequent melting process, which not only increases the risk of metallurgical defects in the titanium alloy melting process, but also poses a major safety risk of causing safety accidents in the melting process. In the prior art, the method of re-remelting and re-welding is usually adopted to solve the cracking problem caused by thermal stress in the welding electrode weld during the cooling process. The method of re-furnace welding is to take the welding electrode out of the furnace after cooling for 120 minutes, check the weld quality of the welding electrode, mark the cracked position of the weld, and re-install the electrode into the welding box, and then evacuate the welding box, fill it with argon gas, weld at the marked position, and cool it out of the furnace. The method of re-furnace welding has the following disadvantages: The repair welding process takes a long time, and the weld may continue to crack during the repair welding process. It may need to be re-melted and repaired several times, which will cost more man-hours and argon gas, increase production costs, and reduce production efficiency. The repair welding process requires the use of plasma arc lighting to manually operate the welding torch to repair the cracked position. This process is very likely to miss the cracked position during the remelting process, causing safety risks in the melting process; The re-melting and re-welding process requires taking out of the furnace and loading into the furnace, which will prolong the storage time of the welding electrode in the air, which will also cause the welding electrode to absorb more moisture and affect the oxygen content of the final product. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, an object of the present invention is to provide a welding method for reducing weld cracks in titanium alloy welding electrodes, which can reduce re-melting welding.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows: A welding method for reducing weld cracks in titanium alloy welding electrodes, characterized in that it comprises the following steps: Step 1), stacking 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 applying axial pressure on the end surface; Specifically, the pressed electrode is a round cake-shaped electrode pressed by a hydraulic press. The electrode diameter applicable to the present 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 the appropriate pressure is selected according to the size of the gap.

[0006] Step 2) Use the trolley attached to the vacuum plasma welding box to deliver the stacked electrode after step 1 into the welding box, and adjust the position of the stacked electrode head to just below the welding gun, and define this place as the welding zero point and angle zero point; then start to evacuate the vacuum to ≤10Pa, and perform leak detection after the vacuum is in place, requiring the leak rate to be ≤1Pa / min; when all vacuum conditions meet the standards, fill the welding box with argon gas, and control the argon gas pressure at 30000-60000Pa; Specifically, titanium, as an active metal, is very easy to react with elements such as O and N in the air. Titanium welding needs to be carried out under argon protection. Evacuating the vacuum plasma welding box and setting a certain leakage rate can prevent the electrode from oxidizing during the welding process. The vacuum plasma welding box needs to be in an argon atmosphere with 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 process is carried out according to the set position and angle.

[0007] Step 3) Set the conventional welding parameters, specifically the welding current is 200-700A, the welding voltage is 40-90V, the argon gas flow rate is 5-30L / min, the welding speed is 30-100mm / min, turn on the automatic welding mode, start welding the first weld, and when welding to the bottom of the electrode, turn off the welding and lift the welding gun; The welding parameters of this step are conventional welding methods based on 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 electrode is pressed into a solid state, and the increased density will cause the weld to shrink. The resulting welding speed should not be too large, as it will easily lead to unconcentrated welding heat, insufficient weld depth, and the weld only on the electrode surface, resulting in insufficient weld strength. The welding speed should not be too small, as it will lead to concentrated heat during the welding process, a deeper weld pool, more severe shrinkage when the weld pool solidifies, and concentrated weld thermal stress, resulting in electrode bending and weld cracking. The weld based on the above welding parameters is a straight line, with a weld depth of ≥30mm and a weld width of ≥30mm. Depending on the length of the electrode, the welding process requires 10-60 minutes for a single weld.

[0008] Step 4), then move the stacked electrode to the welding zero point, reset the welding parameters, use a welding current and welding voltage that are smaller than those used for the first weld, and a welding speed that is faster than that used for the first weld. Specifically, adjust the welding current, voltage, argon gas flow rate and welding speed according to the state of the welding molten pool, so as to achieve the best state when the molten pool is about to be formed but has not been formed. Start the automatic welding mode again, heat the weld at the position of the first weld, and then close the welding program after welding to the bottom of the electrode, lift the welding gun, and move the stacked electrode to the welding zero point; This step is to use a smaller current and voltage, that is, a smaller welding input power, and a faster welding speed after conventional welding of a weld, so as not to melt the original weld and reheat the weld. When the electrode length is long, the temperature difference between the welding zero point and the welding end position is large, and the thermal stress release rate is inconsistent during the cooling process, resulting in weld cracking. The role of this step is to use plasma to reheat the weld, so that the temperature of the entire weld tends to be consistent, and the thermal stress release rate during the cooling process is the same, which is equivalent to a stress relief annealing of the entire weld to reduce weld cracking.

[0009] Step 5), rotate the stacking electrode to 180° of the angle zero point, repeat steps 3), step 4); rotate the stacking electrode again to 270° of the angle zero point, repeat steps 3), step 4); rotate the stacking electrode again to 90° of the angle zero point, repeat steps 3), step 4); rotate the stacking electrode again to 315° of the angle zero point, repeat steps 3), step 4); rotate the stacking electrode again to 135° of the angle zero point, repeat steps 3), step 4); rotate the stacking electrode again to 45° of the angle zero point, repeat steps 3), step 4); rotate the stacking electrode again to 225° of the angle zero point, repeat steps 3), step 4); then rotate the stacking electrode to the angle zero point, and move the stacking electrode to the welding zero point; The operation process of this step is to repeat steps 3 and 4 after the electrode is rotated a certain angle. The welding process is welded according to a certain angle distribution, mainly for symmetrical welding, that is, after welding one weld, weld the next weld at 180°. When a weld is completed, the shrinkage of the weld will cause the electrode on that side to bend inward and be subjected to compressive stress, while the electrode on the 180° symmetrical side is subjected to tensile stress, which eventually causes the electrode to bend into a bow shape. After welding one weld, welding the next weld on the 180° symmetrical side can correct the electrode bending caused by the previous weld in the opposite direction to make the electrode straighter. In addition, the purpose of evenly distributing the 8 welds on the electrode at 45° is to evenly release the stress of the weld shrinkage, so that the electrode straightness is better, and there will be no stress concentration caused by local weld concentration, which will cause the weld to crack.

[0010] Step 6), resetting the welding parameters, using a welding current and welding voltage less than that used in step 4), and a faster welding speed than that used in step 4), specifically adjusting the welding current, voltage, argon gas flow rate and welding speed according to the state of the molten pool, so as to heat purge the weld without causing the weld to melt for the best, restarting the welding program at the welding zero point, allowing the plasma welding gun to heat purge the position of the first weld until the bottom of the electrode, and then moving the stacked electrode to the welding zero point; Compared with step 4, step 6 uses lower welding current, voltage and faster welding speed, and its purpose is similar to step 4. In step 5, the welding of all 8 welds has been completed, but it has lasted 200 to 480 minutes from the start of welding of the first weld to the completion of welding of the eighth weld. The cooling time of the first weld is 200 to 480 minutes longer than that of the eighth weld, and there is a significant difference in the degree of welding thermal stress release. This step uses a lower power plasma to purge and heat the 8 welds in sequence, so that the temperature of the 8 welds is increased and cooled at a more uniform temperature, which is equivalent to performing a lower temperature stress relief annealing on the welds at a lower temperature, thereby reducing weld cracking.

[0011] Step 7), rotate the stacked electrode to 45°, 90°, 135°, 180°, 225°, 270°, 315° at the angle zero point in turn, and repeat step 6); close the welding program, lift the welding gun, and move the stacked electrode to the welding zero point.

[0012] Step 8), evacuate the welding box to 10-100Pa, then turn off the vacuum pump unit, break the welding box after at least 120 minutes, take out the electrode, and check the quality of the electrode weld; This step is the vacuum cooling process of the welding electrode. The purpose of evacuating the vacuum plasma welding box after welding is to reduce the cooling rate of the welding electrode. When the atmosphere in the welding box is 30000~60000Pa of the working atmosphere, the argon medium in the welding box will cause the electrode to have a large heat dissipation capacity, the cooling rate of the weld is too large, and the thermal stress is released quickly, resulting in weld cracking. In this step, the argon gas in the welding box is evacuated to 10-100Pa, reducing the argon medium in the welding box, which is conducive to reducing the cooling rate of the weld and reducing the probability of weld cracking. The cooling time of this step is controlled to be more than 120min, so that the weld has sufficient time to slowly release stress and avoid electrode cracking.

[0013] Preferably, in the above step 1), after all the electrode blocks are stacked, axial pressure is applied to the end surface so that the gap between two adjacent electrode blocks is controlled to be 1-5 mm.

[0014] Preferably, in the above step 4), the welding current is 100-600A, the welding voltage is 30-80V, the argon gas flow rate is 5-30L / min, and the welding speed is 60-100mm / min.

[0015] Preferably, in the above step 6), the welding current is 100-500A, the welding voltage is 30-70V, the argon gas flow rate is 5-30L / min, and the welding speed is 80-120mm / min.

[0016] Compared with the prior art, the present invention has the following beneficial effects: By adopting the method of the present invention, the welding thermal stress can be fully released during the welding process, so as to avoid the weld seam from cracking during the cooling process, and finally achieve the purpose of not needing to re-melt for repair welding. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a physical picture of the welding quality of comparative example 1 of the present invention; Figure 2 This is a physical picture of the welding quality of comparative example 2 of the present invention; Figure 3 This is a physical picture of the welding quality of the first embodiment of the present invention. DETAILED DESCRIPTION

[0018] The technical scheme of the present invention is further described in detail below in conjunction with specific examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention. Specific examples are provided below to describe the method of the present application, and other preparation parameters not mentioned in each example remain consistent in all examples.

[0019] It should be understood that the purpose of providing these embodiments is to make the disclosure of the present invention more thoroughly understood. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention.

[0020] Pressed electrodes are made of a mixture of titanium sponge and master alloy and pressed into regular electrode blocks by a hydraulic press. Depending on the pressure of the press, the density of the electrode block is between 3.0 and 3.7 g / cm 3 The welding process of the electrode block relies on high-temperature plasma to melt part of the electrode surface and then solidify to form a weld to achieve the purpose of connecting the electrode blocks. Although the sponge titanium and the intermediate alloy have been pressed by the hydraulic press, the density of the solidified titanium alloy is 4.5g / cm 3 Compared with the conventional welding machine, there is still a large density difference, and the electrode strength in the solidified state is significantly higher than that in the pressed state. This density difference and strength difference can easily lead to cracking in the process of thermal stress release of the weld. In addition, the gap between the stacked electrode blocks cannot be too small or too large. During the solidification of the welding molten pool, the increased density will cause the weld to shrink. If the gap is too small, the shrinkage distance will be insufficient, causing weld cracks. The gap cannot be too large. If the gap is too large, the melt in the molten pool will flow along the gap between the electrode blocks, and the molten pool will not be full, resulting in a cold weld. The present invention has verified through multiple experiments that the gap of 1 to 5 mm can meet the requirements of weld shrinkage and fullness of the molten pool.

[0021] Comparative Example 1 Step 1), stack the TC4 Φ420×4400mm electrodes on the rollers of the vacuum plasma welding box, apply axial compressive stress, and control the electrode gap to 1-5mm; Step 2) Use the trolley attached to the vacuum plasma welding box to drive the stacked electrode blocks into the box, adjust the position of the electrode head to just below the welding gun and set it as the welding zero point and angle zero point. Then start to evacuate the vacuum to ≤10Pa, and perform leak detection after the vacuum is in place, requiring the leak rate to be ≤1Pa / min. When all vacuum conditions are met, flush argon into the welding box, and the argon pressure is controlled at 30000-60000Pa; Step 3) Set the welding parameters, welding current 200-700A, welding voltage 40-90V, argon gas flow 5-30L / min, welding speed 30-100mm / min, then start the welding program, turn on the automatic welding mode and start welding the first weld. When welding to the bottom of the electrode, close the welding program and lift the welding gun; Step 4), rotate the electrode to 180° of the angle zero point, repeat step 3; rotate the electrode to 270° of the angle zero point again, repeat step 3; rotate the electrode to 90° of the angle zero point again, repeat step 3; rotate the electrode to 315° of the angle zero point again, repeat step 3; rotate the electrode to 135° of the angle zero point again, repeat step 3; rotate the electrode to 45° of the angle zero point again, repeat step 3; rotate the electrode to 225° of the angle zero point again, repeat step 3; rotate the welding electrode to the welding angle zero point, and move the trolley to the welding zero point; Step 5) Turn on the vacuum pump unit of the vacuum plasma welding box, draw the vacuum in the welding box to 10-100Pa, then turn off the vacuum pump unit. After at least 120 minutes, vent the welding box, take the electrode out of the trolley, and check the weld quality of the welding electrode.

[0022] The welding quality of this comparative example is as follows Figure 1 As shown in the figure, the electrode is severely bent and the weld is obviously cracked.

[0023] Comparative Example 2 Step 1), stack the TC4 Φ420×4400mm electrodes on the rollers of the vacuum plasma welding box, apply axial compressive stress, and control the electrode gap to 1-5mm; Step 2) Use the trolley attached to the vacuum plasma welding box to drive the stacked electrode blocks into the box, adjust the position of the electrode head to just below the welding gun and set it as the welding zero point and angle zero point. Then start to evacuate the vacuum to ≤10Pa, and perform leak detection after the vacuum is in place, requiring the leak rate to be ≤1Pa / min. When all vacuum conditions are met, flush argon into the welding box, and the argon pressure is controlled at 30000-60000Pa; Step 3) Set the welding parameters, welding current 200-700A, welding voltage 40-90V, argon gas flow 5-30L / min, welding speed 30-100mm / min, then start the welding program, turn on the automatic welding mode and start welding the first weld. When welding to the bottom of the electrode, close the welding program and lift the welding gun.

[0024] Step 4) Move the trolley to the welding zero point, reset the welding parameters, welding current 100-600A, welding voltage 30-80V, argon gas flow 5-30L / min, welding speed 60-100mm / min, and start the welding program at the welding zero point. Start the automatic welding mode again, until the bottom of the electrode is welded, close the welding program, and lift the welding gun. Move the trolley to the welding zero point.

[0025] Step 5), rotate the electrode to 180° at the angle zero point, repeat steps 3 and 4; rotate the electrode to 270° at the angle zero point again, repeat steps 3 and 4; rotate the electrode to 90° at the angle zero point again, repeat steps 3 and 4; rotate the electrode to 315° at the angle zero point again, repeat steps 3 and 4; rotate the electrode to 135° at the angle zero point again, repeat steps 3 and 4; rotate the electrode to 45° at the angle zero point again, repeat steps 3 and 4; rotate the electrode to 225° at the angle zero point again, repeat steps 3 and 4; rotate the welding electrode to the welding angle zero point, and move the trolley to the welding zero point.

[0026] Step 6) Turn on the vacuum pump unit of the vacuum plasma welding box, draw the vacuum in the welding box to 10-100Pa, then turn off the vacuum pump unit. After at least 120 minutes, vent the welding box, take the electrode out of the trolley, and check the weld quality of the welding electrode.

[0027] The difference between the comparative example 2 and the comparative example 1 is that the stress relief annealing welding in step 4 is added after the welding of one weld. Figure 2 The electrode is not bent, but there are still small cracks in the weld. Example

[0028] Step 1), stack the TC4 Φ420×4400mm electrodes on the rollers of the vacuum plasma welding box, apply axial compressive stress, and control the electrode gap to 1-5mm; Step 2) Use the trolley attached to the vacuum plasma welding box to drive the stacked electrode blocks into the box, adjust the position of the electrode head to just below the welding gun and set it as the welding zero point and angle zero point. Then start to evacuate the vacuum to ≤10Pa, and perform leak detection after the vacuum is in place, requiring the leak rate to be ≤1Pa / min. When all vacuum conditions are met, flush argon into the welding box, and the argon pressure is controlled at 30000-60000Pa; Step 3) Set the welding parameters, welding current 200-700A, welding voltage 40-90V, argon gas flow 5-30L / min, welding speed 30-100mm / min, then start the welding program, turn on the automatic welding mode and start welding the first weld. When welding to the bottom of the electrode, close the welding program and lift the welding gun; Step 4) Move the trolley to the welding zero point, reset the welding parameters, welding current 100-600A, welding voltage 30-80V, argon gas flow 5-30L / min, welding speed 60-100mm / min, and start the welding program at the welding zero point. Start the automatic welding mode again, until the bottom of the electrode is welded, close the welding program, and lift the welding gun. Move the trolley to the welding zero point.

[0029] Step 5), rotate the electrode to 180° at the angle zero point, repeat steps 3 and 4; rotate the electrode to 270° at the angle zero point again, repeat steps 3 and 4; rotate the electrode to 90° at the angle zero point again, repeat steps 3 and 4; rotate the electrode to 315° at the angle zero point again, repeat steps 3 and 4; rotate the electrode to 135° at the angle zero point again, repeat steps 3 and 4; rotate the electrode to 45° at the angle zero point again, repeat steps 3 and 4; rotate the electrode to 225° at the angle zero point again, repeat steps 3 and 4; rotate the welding electrode to the welding angle zero point, and move the trolley to the welding zero point.

[0030] Step 6) Reset the welding parameters, welding current 100-500A, welding voltage 30-70V, argon flow 5-30L / min, welding speed 80-120mm / min, adjust the welding current, voltage, argon flow and welding speed according to the state of the molten pool, start the welding program at the welding zero point position, so that the plasma sweeps over the weld until the bottom of the welding electrode. Move the trolley to the welding zero point.

[0031] Step 7) Rotate the electrode to the zero angle of 45°, 90°, 135°, 180°, 225°, 270°, and 315° in sequence, and repeat step 6. Close the welding program, lift the welding gun, and move the carriage to the zero position.

[0032] Step 8) Turn on the vacuum pump unit of the vacuum plasma welding box, draw the vacuum in the welding box to 10-100Pa, then turn off the vacuum pump unit. After at least 120 minutes, vent the welding box, take the electrode out of the trolley, and check the weld quality of the welding electrode.

[0033] The difference between the first embodiment and the second comparative embodiment is that the stress relief annealing welding in step 6 is added after the eight welds are welded. Figure 3 As shown in the figure, the electrode has good straightness and the weld does not crack.

Claims

1. A welding method for reducing weld cracks in titanium alloy welding electrodes, characterized in that: The steps include: Step 1), stacking 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 being 1000-7000mm; Step 2), use a vacuum plasma welding box to weld, put the stacked electrode after step 1 into the welding box and adjust the position of the stacked electrode head to just below the welding gun, and define this place as the welding zero point and angle zero point; evacuate the box, and then fill it with argon gas, and the argon gas pressure is controlled at 30000-60000Pa; Step 3), start welding the first weld using conventional methods, and when welding to the bottom of the electrode, close the welding; Step 4), move the stacking electrode to the welding zero point, use a welding current and welding voltage smaller than that used for the first weld, and a welding speed faster than that used for the first weld, and heat the weld again at the position of the first weld. After completion, move the stacking electrode to the welding zero point; Step 5), rotate the stacking electrode to 180° of the angle zero point, repeat steps 3), step 4); rotate the stacking electrode again to 270° of the angle zero point, repeat steps 3), step 4); rotate the stacking electrode again to 90° of the angle zero point, repeat steps 3), step 4); rotate the stacking electrode again to 315° of the angle zero point, repeat steps 3), step 4); rotate the stacking electrode again to 135° of the angle zero point, repeat steps 3), step 4); rotate the stacking electrode again to 45° of the angle zero point, repeat steps 3), step 4); rotate the stacking electrode again to 225° of the angle zero point, repeat steps 3), step 4); then rotate the stacking electrode to the angle zero point, and move the stacking electrode to the welding zero point; Step 6), using a welding current and welding voltage less than that used in step 4), and a welding speed faster than that used in step 4), heat purging is performed at the position of the first weld, and after completion, the stacked electrode is moved to the welding zero point; Step 7), rotate the stacking electrode to 45°, 90°, 135°, 180°, 225°, 270°, 315° of the angle zero point in turn and repeat step 6); after completion, move the stacking electrode to the welding zero point; Step 8) Evacuate the welding box to 10-100Pa, then turn off the vacuum pump unit, and remove the electrode from the welding box after cooling for a period of time.

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

3. A welding method for reducing weld cracks in titanium alloy welding electrodes according to claim 1 or 2, characterized in that: In the above step 4), the welding current is 100-600A, the welding voltage is 30-80V, the argon gas flow rate is 5-30L / min, and the welding speed is 60-100mm / min.

4. A welding method for reducing weld cracks in titanium alloy welding electrodes according to claim 3, characterized in that: In the above step 6), the welding current is 100-500A, the welding voltage is 30-70V, the argon gas flow rate is 5-30L / min, and the welding speed is 80-120mm / min.

5. A welding method for reducing weld cracks in titanium alloy welding electrodes according to claim 4, characterized in that: The cooling time in the above step 8) is at least 120 minutes.

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