Titanium alloy pressed electrode welding method

Abstract

The invention relates to the technical field of titanium alloy processing, and particularly discloses a titanium alloy pressed electrode welding method, which comprises the following steps of: sequentially applying a spot welding at a joint position between every two adjacent cake-shaped electrode blocks on an integral electrode from one end to the other end in the length direction of the integral electrode, and keeping the welding spots of the spot welding on the same straight line; then, all the cake-shaped electrode blocks related to the whole electrode are rolled by 20 degrees in the circumferential direction of the whole electrode, spot welding is sequentially applied to the joint position between every two adjacent cake-shaped electrode blocks from one end to the other end in the length direction of the whole electrode, and welding spots of the spot welding need to be kept on the same straight line; and after spot welding is completed, the whole electrode is subjected to multiple times of clockwise rotation, then short welding line direct welding operation is conducted, and the welding length of the short welding line is controlled to be not larger than 1500 mm. By the adoption of the method, the length of the weldable electrode can be greatly increased, the number of smelting electrodes can be reduced, and the risk of inclusion and air holes caused by butt welding of the primary ingot and the secondary ingot is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of metal smelting and casting, and particularly relates to a welding method for a consumable vacuum melting pressed electrode of a titanium alloy. Background Art

[0002] At present, the typical smelting method of titanium alloy at home and abroad is consumable vacuum melting. Its smelting method requires that the powdery or granular raw materials are first pressed into electrode blocks of the required shape by a large-tonnage extrusion device, and then welded into an integral electrode by welding equipment such as a vacuum plasma welding box. Finally, the integral electrode is transferred into the crucible of a consumable vacuum furnace, and the ingot is prepared by the method of consumable melting. The integral electrode is usually composed of multiple electrode blocks spliced together. Taking the commonly used disc-shaped electrode blocks in China as an example, usually one electrode is spliced by 15 - 30 electrode blocks, and then integrated through multiple passes of welding by a vacuum plasma welding box. During the welding process, the vacuum plasma welding box can only complete the welding of one weld line at a time, and multiple weld lines are welded in sequence one by one. However, with the solidification of the welding pool of the previously welded weld line and the thermal expansion and contraction of the weld line part, the electrode usually has the following two defects: ① The electrode is bent due to the influence of the unilateral shrinkage of the weld line; ② The internal stress generated by the shrinkage of the weld line exceeds the load-bearing limit of the weld line, and the weld line breaks. The above two defects will gradually intensify with the increase of the electrode length, and will pose great potential safety hazards in the subsequent smelting process. The former is likely to cause side arcs and penetrate the crucible; the latter will cause the electrode to break during the smelting process, and the electrode will fall and damage the crucible, causing water seepage. Both have the risk of explosion. The method of pre-clamping before welding can alleviate the generation of bending and fracture defects, but still cannot fundamentally solve this problem. This leads to the fact that large ingots need to be welded and remelted from multiple small ingots, which not only increases the risks of ingot inclusions, pores, etc., but also limits the single weight of the ingot, having a certain impact on the development of the domestic aviation industry. Therefore, it is of great significance to develop an electrode welding method that can avoid electrode bending and weld line cracking and improve the length of the weldable electrode. Summary of the Invention

[0003] Aiming at the deficiencies of the above-mentioned existing technologies, the purpose of the present invention is to provide a welding method for a titanium alloy pressed electrode. The theoretical basis of this method is that the internal stress generated by the solidification of the welding pool and the thermal expansion and contraction of the material is positively correlated with the size of the material generating the internal stress, that is, the larger the size of continuous solidification or thermal expansion and contraction, the greater the generated internal stress. In the welding electrode, it is manifested that the longer the size of the weld line, the greater the generated internal stress. Therefore, one of the effective ways to relieve internal stress is to reduce the length of a single weld line, and the function of a single long weld line is realized through the coordinated combination of multiple short weld lines.

[0004] To achieve the above purpose, the technical solution adopted by the present invention is as follows: A welding method for a titanium alloy pressed electrode, characterized in that it is realized through the following steps: Step 1): Arrange multiple disc-shaped electrode blocks required for the overall electrode horizontally on the idler rollers of the vacuum plasma welding box, and keep the central axis of each disc-shaped electrode block parallel to the arrangement direction of the disc-shaped electrode row. Adjacent two electrode blocks are closely attached to each other. Step 2): Complete the evacuation and argon filling operations of the vacuum plasma welding box according to the conventional welding process. Step 3): Apply a spot weld in sequence at the joint position between every two adjacent disc-shaped electrode blocks from one end to the other end in the length direction of the overall electrode. The weld spots of the aforementioned spot welds need to be kept on the same straight line. Step 4): Rotate all the disc-shaped electrode blocks involved in the overall electrode 20° along the circumferential direction, and again apply a spot weld in sequence at the joint position between every two adjacent disc-shaped electrode blocks from one end to the other end in the length direction of the overall electrode. The weld spots of the aforementioned spot welds also need to be kept on the same straight line. Step 5): After the spot welding is completed, perform straight welding of short weld lines after rotating the overall electrode clockwise multiple times, and control the welding length of the short weld lines not to exceed 1500 mm. Ensure that multiple short weld lines obtained by straight welding at the same rotation angle are on the same straight line after each rotation, and the short weld lines on adjacent two straight lines overlap in the length direction of the overall electrode.

[0005] Furthermore, the specific operation of the rotational straight welding in the above Step 5) is as follows: The first step is to perform straight welding after rotating the overall electrode clockwise by 180°; the second step, rotate 180° clockwise and perform straight welding; the third step, rotate 90° clockwise and perform straight welding; the fourth step, rotate 180° clockwise and perform straight welding; the fifth step, rotate 45° clockwise and perform straight welding; the sixth step, rotate 180° clockwise and perform straight welding; the seventh step, rotate 90° clockwise and perform straight welding; the eighth step, rotate 180° clockwise and perform straight welding.

[0006] Furthermore, in Step 5), in the first step, the second step, the third step, and the fourth step, the welding torch of the vacuum plasma welding box starts to strike an arc at a position about 50 mm away from the outer end of the corresponding disc-shaped electrode block, and the continuous welding length does not exceed 1500 mm, and then stops arcing. If the welding electrode is relatively long and there are many welding torches of the equipment (here, taking the commonly used three-torch welding box as an example, which does not represent that this patent is restricted by the equipment model and status, the same below), the 2# welding torch and the 3# welding torch can strike an arc on the electrode simultaneously, and from the arc starting position, the continuous welding length does not exceed 1500 mm. After the first pass of welding wire is welded, the distribution of the welding wires on the electrode is as follows Figure 1 shown. Except for the different rotation angles of the electrode in the first to the fourth steps, the welding method is the same as that in the first step.

[0007] Steps 5, 6, 7, and 8 require starting the arc at the overlapping position of 300 - 500 mm with the wire bonding in Steps 1 to 4, and the continuous welding length does not exceed 1500 mm (the head and tail of the wire bonding in Steps 5 to 8 overlap with that in Steps 1 to 4 by 300 - 500 mm), and then extinguish the arc. If the welding electrode is long and there are many welding torches on the equipment, the 2# and 3# welding torches can start the arc on the electrode simultaneously. Starting from the arc starting position, the continuous welding length does not exceed 1500 mm. The welding method in Step 5 is as Figure 2 shown. For Steps 6 to 8, except for the different rotation angles of the electrode, the welding method is the same as that in Step 5.

[0008] Compared with the prior art, the beneficial effects of the present invention are as follows: It can greatly reduce the internal stress generated by the solidification of the wire bonding and thermal expansion and contraction, and avoid the bending or cracking of the electrode; By adopting the method of the present invention, the length of the weldable electrode can be greatly increased, the number of smelting electrodes can be reduced, and the risk of inclusions and pores introduced by the butt welding of the primary ingot and the secondary ingot can be reduced; The present invention is beneficial to improving the fixed weight of the ingot and meeting the requirements for the preparation of large-sized materials; The present invention does not require major adjustments to the existing welding method and welding equipment, and can be realized on the existing equipment; The present invention does not require additional clamping tooling, and only needs to stack the electrode blocks in sequence and fit them together. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 It is a schematic diagram of the wire bonding in Steps 1 to 4; Figure 2 It is a schematic diagram of the wire bonding in Steps 5 to 8 (where the short wire bonding on the upper straight line is that in Steps 1 to 4, and the short wire bonding on the lower straight line is that in Steps 5 to 8); Figure 3 It is a schematic diagram of typical long seam welding in the prior art; Figure 4 It is a schematic diagram of the wire bonding in Steps ①②③④⑤⑥⑦⑧ in Step 7) of Embodiment 1 of the present invention; Figure 5 It is a schematic diagram of the wire bonding distribution in Comparative Example 1 related to the present invention;

[0010] Figure 6 It is a wire bonding morphology diagram of Embodiment 1 and Comparative Example 1 of the present invention, where the left side is that of Embodiment 1 and the right side is that of Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention will be described in detail below in combination with the examples of the application of the present invention, so that the advantages and features of the present invention are more easily understood by those skilled in the art, thereby making the protection scope of the present invention clearer and more definite.

[0012] Example 1 In this example, the test object is a TC18 alloy electrode with a specification of Φ420mm. The total length of the electrode is 4707mm, and the number of electrode blocks is 24 (i.e., the overall electrode is 24 layers).

[0013] The specific welding process is as follows: Step 1): Press the electrode into a Φ420mm disc-shaped electrode block. The weight of the electrode block is 92±0.5kg, and the height of the electrode block is 200±5mm; Step 2): Arrange all the disc-shaped electrode blocks horizontally on the roller of the vacuum plasma welding box, and keep the central axis of each disc-shaped electrode block parallel to the arrangement direction of the disc-shaped electrode row. Adjacent two electrode blocks are closely attached without clamping; Step 3): Evacuate the vacuum plasma welding to a vacuum degree ≤8Pa and a leak rate ≤0.8Pa / min, and then fill the welding box with argon at 30000 - 55000Pa; Step 4): Apply a spot weld at the joint position between every two adjacent disc-shaped electrode blocks in sequence from one end to the other end along the length direction of the overall electrode. The weld spots of the aforementioned spot welds need to be kept on the same straight line; Step 5): Rotate all the disc-shaped electrode blocks involved in the overall electrode clockwise by 20° along the circumferential direction. Again, from one end to the other end along the length direction of the overall electrode, apply a spot weld at the joint position between every two adjacent disc-shaped electrode blocks in sequence. The weld spots of the aforementioned spot welds also need to be kept on the same straight line; Step 6): Presuppose to replace 4 long weld lines as an example, and presuppose that the length of a single weld line is not greater than 1350mm; Step 7): After the spot welding is completed, rotate the overall electrode clockwise by 180° for straight welding. The specific sequence is: rotate clockwise by 180° for straight welding ①→rotate clockwise by 180° for straight welding ②→rotate clockwise by 90° for straight welding ③→rotate clockwise by 180° for straight welding ④→rotate clockwise by 45° for straight welding ⑤→rotate clockwise by 180° for straight welding ⑥→rotate clockwise by 90° for straight welding ⑦→rotate clockwise by 180° for straight welding ⑧. Among them, the specific welding of ①②③④ is as Figure 4 follows: The 1# welding torch starts to arc at about 50mm from the 1st electrode and extinguishes the arc at the 7th electrode (about 1400mm); The 2# torch starts to arc on the 11th electrode (about 2050mm) and extinguishes the arc on the 18th electrode (about 3400mm); The 3# torch starts to arc on the 22nd electrode (about 4050mm) and extinguishes the arc on the last electrode block. The welding of ⑤⑥⑦⑧ is carried out according to Figure 4Procedure: 1# The welding torch starts arcing at the 6th electrode (at approximately 1050 mm) and stops arcing at the 12th electrode (at approximately 2400 mm). The head and tail of the welding wire are each staggered by 350 mm with the welding wires ①②③④; 2# The welding torch starts arcing at the 17th electrode (at approximately 3050 mm) and stops arcing at the 23rd electrode (at approximately 4400 mm). The head and tail of the welding wire are each staggered by 350 mm with the welding wires ①②③④. Due to the limitation of the electrode length, the 3# welding torch does not participate in the welding during the welding process of ⑤⑥⑦⑧.

[0014] The electrode quality of this first embodiment is shown in Table 1.

[0015] Comparative Example 1 The test object selected in this comparative example is also a TC18 alloy electrode with a Φ420 mm specification. The total length of the electrode is 4707 mm, and the number of electrode blocks is 24 (i.e., the overall electrode is 24 layers).

[0016] Step 1): Press the electrode into a Φ420 mm disc-shaped electrode block. The weight of the electrode block is 92 ± 0.5 kg, and the height of the electrode block is 200 ± 5 mm. Step 2): Arrange all the disc-shaped electrode blocks horizontally on the rollers of the vacuum plasma welding box, and keep the central axis of each disc-shaped electrode block parallel to the arrangement direction of the disc-shaped electrode row. The adjacent two electrode blocks are closely attached to each other without clamping. Step 3): Vacuum the vacuum plasma welding to a vacuum degree ≤ 8 Pa and a leak rate ≤ 0.8 Pa / min, and then fill the welding box with argon at 30000 - 55000 Pa. Step 4): Apply a spot weld to the seam position between every two adjacent disc-shaped electrode blocks in sequence from one end to the other end of the overall electrode in the length direction. The weld spots of the aforementioned spot welds need to be kept on the same straight line. Step 5): Rotate all the disc-shaped electrode blocks involved in the overall electrode clockwise by 20° along the circumferential direction. Again, from one end to the other end of the overall electrode in the length direction, apply a spot weld to the seam position between every two adjacent disc-shaped electrode blocks in sequence. The weld spots of the aforementioned spot welds also need to be kept on the same straight line. Step 6): After the spot welding is completed, perform a conventional straight weld on the long welding wire of the electrode. The sequence is ① rotate clockwise by 180° and perform a straight weld (the 1# gun starts arcing at 50 mm of the electrode and stops arcing at 2100 mm, the 2# welding torch starts arcing at 2050 mm and stops arcing at 4100 mm, the 3# welding torch starts arcing at 4050 mm and stops arcing at 4650 mm, and ②③④ are the same) → ② rotate clockwise by 180° and perform a straight weld → ③ rotate clockwise by 90° and perform a straight weld → ④ rotate clockwise by 180° and perform a straight weld.

[0017] The electrode quality of this Comparative Example 1 is shown in Table 1 .

Claims

1. A method for welding a titanium alloy pressing electrode, characterized in that, It is achieved through the following steps: Step 1): Arrange multiple disc-shaped electrode blocks required for the overall electrode horizontally on the rollers of the vacuum plasma welding box, and keep the central axis of each disc-shaped electrode block parallel to the arrangement direction of the disc-shaped electrode row. Adjacent two electrode blocks are closely attached to each other; Step 2): Complete the vacuum pumping and argon filling operations of the vacuum plasma welding box according to the conventional welding process; Step 3): Apply a spot weld in sequence at the joint position between every two adjacent disc-shaped electrode blocks from one end to the other end of the overall electrode in its length direction. The welding spots of the aforementioned spot welds need to be kept on the same straight line; Step 4): Rotate all the disc-shaped electrode blocks involved in the overall electrode 20° along its circumferential direction. Again, from one end to the other end of the overall electrode in its length direction, apply a spot weld in sequence at the joint position between every two adjacent disc-shaped electrode blocks. The welding spots of the aforementioned spot welds also need to be kept on the same straight line; Step 5): After the spot welding is completed, rotate the overall electrode clockwise multiple times and then perform straight welding on the short weld lines, and control the welding length of the short weld lines not to exceed 1500 mm, ensuring that multiple short weld lines obtained by straight welding at the same rotation angle after each rotation are on the same straight line, and the short weld lines on adjacent two straight lines overlap in the length direction of the overall electrode.

2. The method for welding a titanium alloy pressing electrode according to claim 1, wherein The specific operations in the above Step 5) are as follows: The first step is to rotate the overall electrode clockwise by 180° and then perform straight welding; the second step, rotate clockwise by 180° and perform straight welding; the third step, rotate clockwise by 90° and perform straight welding; The fourth step, rotate clockwise by 180° and perform straight welding; The fifth step, rotate clockwise by 45° and perform straight welding; The sixth step, rotate clockwise by 180° and perform straight welding; The seventh step, rotate clockwise by 90° and perform straight welding; The eighth step, rotate clockwise by 180° and perform straight welding.

3. A method for welding a titanium alloy pressing electrode according to claim 1, characterized in that, In Step 5), in the first step, the second step, the third step, and the fourth step, the welding torch of the vacuum plasma welding box starts to strike an arc on the corresponding disc-shaped electrode block and about 50 mm away from its outer end; while in the fifth step, the sixth step, the seventh step, and the eighth step, it is required to start striking an arc at the overlapping position of 300 - 500 mm with the weld lines obtained in the first step to the fourth step.

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