A waveform control method for reducing the spatter rate of titanium alloy GMAW-P welding

Abstract

The present application belongs to the technical field of welding, and discloses a waveform control method for reducing the spatter rate of titanium alloy GMAW-P welding. The traditional GMAW-P current waveform is improved by adding a separate pulse and prolonging the base value time, so that the titanium alloy GMAW-P current waveform is divided into three stages: the base value stage, the main pulse stage and the separate pulse stage. The present application gives the droplet a greater transition speed and a wider time range, so that it contacts the molten pool and completes the transition in the base value stage, and the titanium alloy droplet with higher surface tension will not be ejected outward under the action of strong cathode jet when it contacts the molten pool, thereby greatly reducing the welding spatter rate. The present application can make the GMAW-P current waveform more suitable for the physical characteristics of titanium alloy, such as higher surface tension and strong cathode jet, thereby promoting the application of GMAW-P process in titanium alloy welding and significantly improving the production efficiency of titanium alloy structural parts.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of welding, and in particular, relates to a waveform control method for reducing the spatter rate of titanium alloy pulsed gas metal arc welding (GMAW-P), mainly solving the problem of serious spatter generated in the titanium alloy GMAW-P welding process. BACKGROUND

[0002] Titanium alloy has low density, high strength and excellent corrosion resistance, and is widely used in aerospace, automobile manufacturing and marine vessels [1][2][3] . With the rapid growth of demand for large and complex titanium alloy structural parts in these fields, the demand for advanced titanium alloy welding technology has become increasingly urgent. In the prior art, plasma arc welding (PAW) can achieve a larger penetration [4][5] , but the complex welding torch makes it difficult to apply to the corner joint welding situation that exists in large quantities; electron beam welding (EBW) can obtain pure weld metal, but it relies heavily on a vacuum environment; gas tungsten arc welding (GTAW) can adapt to the welding of complex structural parts, but its indirect heating of the arc to melt the welding wire severely limits the welding efficiency [6][7] . In contrast, gas metal arc welding (GMAW) has the ability to adapt to complex welding paths while having very high welding efficiency [8] , and is one of the most promising welding technologies for manufacturing large and complex titanium alloy structural parts.

[0003] So far, the titanium alloy GMAW process has not been widely used in actual production, mainly due to the serious spatter problem generated during the welding process [6][7] . To solve the spatter problem, the prior art attempts to directly use the traditional GMAW-P current waveform with many adjustable parameters for titanium alloy welding. However, the traditional GMAW-P current waveform is mainly used for welding iron alloy, aluminum alloy and other materials, and iron alloy, aluminum alloy and other materials have different welding physical properties than titanium alloy, so the droplet transfer behavior of the two also differs, specifically in the following two points, first, titanium alloy has a higher surface tension, and second, titanium alloy has a strong cathode jet.

[0004] Titanium alloy has a higher surface tension than iron alloy, aluminum alloy and other materials, which makes titanium alloy need a larger current to achieve a fast and stable necking and breaking process. If the traditional GMAW-P current waveform is directly used for titanium alloy welding, it will cause the problem of excessive elongation of the necking, and thus cause the phenomenon of slow droplet transfer speed.

[0005] Cathode jet is a phenomenon of abnormal concentration of cathode electron emission during welding. According to the physical theory of arc, cathode continuously emits electrons to maintain the dynamic balance of arc during welding, which mainly has two basic modes of thermal emission and field emission. The electron emission behavior of most metals is usually dominated by one of the two modes. However, the physical properties (boiling point, work function and emission rate, etc.) of titanium alloy are just in the intermediate range of the triggering conditions of the two emission modes, which makes titanium alloy have the characteristics of both thermal emission and field emission [9] . Specifically, titanium alloy forms a high-brightness cathode spot that only field emission mode can form, and the cathode spot also shows the characteristics of relatively fixed position that only thermal emission mode can have, which leads to the easy concentration of electron emission at the more fixed cathode spot, and then forms a strong and continuous cathode jet

[10]

[11] . Cathode jet will generate an electromagnetic shrinkage force opposite to the direction of droplet transfer when the droplet contacts the molten pool, thereby hindering the droplet transfer.

[0006] Figure 1 The high-speed photography images of droplet transfer are shown, and it can be found that when the traditional GMAW-P current waveform is directly used for titanium alloy welding, serious welding spatter will be generated, which is related to the above two differences. The two differences, i.e. titanium alloy has higher surface tension and strong cathode jet, lead to the mechanism of spatter formation as follows: after the current droplet experiences growth, necking formation and rupture, it begins to transfer in the arc space. The higher surface tension of titanium alloy makes the droplet transfer slower, and the droplet may not be able to contact the molten pool and complete the transfer within the base value stage. If the time point of the droplet contacting the molten pool is not the base value stage but the next pulse stage, as the cathode spot jumps from the molten pool to the droplet with higher temperature, a strong and continuous cathode jet will gradually form at the top of the droplet

[12] . At this time, the huge electromagnetic shrinkage force generated by the high-density welding current through the droplet will rapidly eject part of the droplet out of the molten pool, eventually leading to serious welding spatter as shown in Figure 2 .

[0007] In order to reduce the spatter rate in titanium alloy GMAW-P process, the waveform control method is adopted in the prior art. Zhang et al.

[13] proposed a waveform control method based on GMAW-P, the principle of which is to output a separation pulse rapidly after the excitation pulse ends and enters the base value stage, so that the droplet is rapidly injected into the molten pool under the joint action of the downward electromagnetic force generated by the separation pulse and the downward momentum generated by its own oscillation, thereby realizing the stable one-pulse-one-drop (ODPP) transfer mode. Sun et al.

[14] and Zhou et al.

[15] The cold metal transfer (CMT) technology was introduced to control the current drop and wire retraction during short circuiting transition, which made the droplet complete the transition smoothly under the action of surface tension and significantly reduced the spatter rate during the welding of Ti-6Al-4V components. Lee et al.

[16] Based on the CMT technology, the current at the droplet detachment moment was appropriately increased to promote the rapid fracture after the formation of the neck, avoid the problem of excessive elongation of the neck, and further improve the stability of the short circuiting transition of titanium alloy.

[0008] The existing waveform control methods of titanium alloy GMAW-P can reduce the spatter rate to some extent, but they all have obvious limitations. Zhang et al.

[13] When controlling the droplet detachment in GMAW-P, additional electric signal sensing circuit, signal processing circuit and control circuit are applied, which makes it difficult to apply these complex circuits in the production site that pursues high efficiency and low cost. The introduction of CMT technology

[14]

[15]

[16] can well solve the spatter problem of titanium alloy GMAW, but since it relies only on surface tension to realize droplet transition, the efficiency is low and the penetration is small, so it is mainly used for the welding of thin plates, and has inherent technical limitations in the multi-layer and multi-pass welding of thick plate groove filling.

[0009] [1] Boyer R R. An overview on the use of titanium in the aerospace industry [J]. Materials Science and Engineering: A, 1996, 213(1-2): 103-114.

[0010] [2] Takahashi K, Mori K, Takebe H. Application of titanium and its alloys for automobile parts [C] / / MATEC web of conferences. EDP Sciences, 2020, 321: 02003.

[0011] [3] Ali A, Pan L, Duan L, et al. Characterization of seawater hygrothermal conditioning effects on the properties of titanium-based fiber-metal laminates for marine applications [J]. Composite Structures, 2016, 158: 199-207.

[0012] [4] Zhang Y M, Zhang S B. Observation of the keyhole during plasma arc welding[J]. Welding journal, 1999, 78: 53-s.

[0013] [5] Li X R, Shao Z, Zhang Y M. Double stage plasma arc pipe welding process[J]. Welding journal, 2012, 91: 346-353.

[0014] [6] Pardal G, Martina F. Laser stabilization of GMAW additive manufacturing of Ti-6Al-4V components[J].

[0015] Journal of Materials Processing Technology, 2019, 272: 1-8.

[0016] [7] Choudhury S S, Marya S K, Amirthalingam M. Improving arc stability during wire arc additive manufacturing of thin-walled titanium components[J]. Journal of Manufacturing Processes, 2021, 66: 53-69.

[0017] [8] Hu Z, Hua L, Qin X, et al. Molten pool behaviors and forming appearance of robotic GMAW on complex surface with various welding positions[J]. Journal of Manufacturing Processes, 2021, 64: 1359-1376.

[0018] [9] Shinn B W, Farson D F, Denney P E. Laser stabilisation of arc cathode spots in titanium welding[J].

[0019] Science and Technology of welding and Joining, 2005, 10(4): 475-481.

[0020]

[10] Lee T H, Kam D H, Oh J H, et al. Ti–6Al–4V alloy deposition characteristics at electrode-negative polarity in the cold metal transfer–gas metal arc process[J]. Journal of Materials Research and Technology, 2022.

[0021]

[11] Lee T H, Kim C, Oh J H, et al. Visualization of cathode spot control using laser irradiation and oxide addition in wire arc additive manufacturing of titanium alloys[J]. Journal of Laser Applications, 2022, 34(4): 042024.

[0022]

[12] Eickhoff S T, Eagar T W. Characterization of spatter in low-current GMAW of titanium alloy plate[J].

[0023] Welding journal, 1990, 69(10): 382.

[0024]

[13] Zhang Y M, Li P J. Modified active control of metal transfer and pulsed GMAW of titanium[J]. Welding journal, 2001, 80(2): 54.

[0025]

[14] Sun Z, Lv Y, Xu B, et al. Investigation of droplet transfer behaviours in cold metal transfer (CMT)

[0026] process on welding Ti-6Al-4V alloy [J]. The International Journal of Advanced Manufacturing Technology, 2015, 80(9): 2007-2014.

[0027]

[15] Zhou S, Xie H, Ni J, et al. Metal transfer behavior during CMT-based Wire Arc Additive Manufacturing of Ti-6Al-4V alloy [J]. Journal of Manufacturing Processes, 2022, 82: 159-173.

[0028]

[16] Lee T H, Kang M, Oh J H, et al. Deposition quality and efficiency improvement method for additive manufacturing of Ti-6Al-4V using gas metal arc with CMT [J]. Journal of Materials Processing Technology, 2022, 308: 117720. SUMMARY

[0029] The application focuses on solving the serious spatter problem generated in the GMAW-P welding process of titanium alloy, and provides a waveform control method for reducing the spatter rate of GMAW-P welding of titanium alloy. By adding a separate pulse and prolonging the base value time, the molten droplet is prevented from being shot out under the action of strong cathode jet when it contacts the molten pool, thereby greatly reducing the welding spatter rate.

[0030] In order to solve the above technical problems, the technical scheme is realized as follows:

[0031] The application provides a waveform control method for reducing the spatter rate of a titanium alloy GMAW-P welding process, which improves the conventional GMAW-P current waveform by adding a separation pulse and prolonging the base value time, so that the titanium alloy GMAW-P current waveform is divided into three stages: a base value stage, a main pulse stage and a separation pulse stage.

[0032] The conventional GMAW-P current waveform is divided into two stages: a base value stage and a pulse stage; the pulse stage is equivalent to the main pulse stage in the titanium alloy GMAW-P current waveform.

[0033] Further, the added separation pulse refers to outputting the separation pulse at the same time as the end of the main pulse, so as to realize a rapid and stable neck breaking process, thereby increasing the droplet transfer speed, so that the droplet rapidly falls into the molten pool and completes the transfer in the next base value stage.

[0034] Preferably, the current of the separation pulse is 50-80% of the main pulse current, and the time of the separation pulse is 70-130% of the main pulse time.

[0035] Further, the prolonged base value time refers to prolonging the time of the next base value stage according to the time required for the droplet to separate from the separation to contact the molten pool when the spatter is formed, so as to enable the droplet to smoothly complete the transfer in the obtained next base value stage.

[0036] Preferably, the prolonged base value time is 11-15 ms.

[0037] More preferably, on the basis of a base value current of 40-60 A, a main pulse current of 300-400 A and a main pulse time of 2-3 ms, a separation pulse with a current of 50-80% of the main pulse current and a time of 70-130% of the main pulse time is added, and the base value time is prolonged to 11-15 ms.

[0038] The application has the following beneficial effects:

[0039] In the titanium alloy GMAW-P, the application proposes a waveform control method of adding a separation pulse after the end of the main pulse and prolonging the base value time, so that the current waveform is more suitable for the physical characteristics of the titanium alloy with higher surface tension and strong cathode jet, and the titanium alloy droplet with higher surface tension is prevented from being shot outwards under the action of the strong cathode jet when contacting the molten pool, thereby greatly reducing the welding spatter rate.

[0040] On the one hand, the waveform control method of adding a separation pulse and prolonging the base value time can give the droplet a greater transfer speed and a wider time range, so that the droplet contacts the molten pool and completes the transfer in the base value stage, thereby solving the serious spatter problem in the titanium alloy GMAW-P welding process.

[0041] On the other hand, compared with the currently used low productivity titanium alloy TIG process, the present application can promote the application of GMAW-P process in titanium alloy welding after effectively reducing the spatter rate, thereby significantly improving the production efficiency of titanium alloy structural parts. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 High speed photography of chaotic droplet transfer behavior before waveform control leading to spatter generation;

[0043] Figure 2 Workpiece surface photo for generating severe welding spatter;

[0044] Figure 3 (a) traditional GMAW-P current waveform for welding iron alloy, aluminum alloy and other materials; (b) titanium alloy GMAW-P current waveform proposed by the present application;

[0045] Figure 4 High speed photography of regular droplet transfer behavior after waveform control by the present application;

[0046] Figure 5 Workpiece surface photo after spatter is effectively suppressed. DETAILED DESCRIPTION

[0047] Figure 3 (a) shows the current waveform of traditional GMAW-P for welding iron alloy, aluminum alloy and other materials, which can be divided into two stages: ① base value stage; ② pulse stage. The droplet transfer process aimed to be achieved by traditional GMAW-P current waveform is described as follows: in the current base value stage ①, the droplet volume slowly increases; in the pulse stage ②, the droplet volume rapidly increases to a critical value, then liquid necking is formed between solid wire and liquid droplet and gradually elongates until it breaks, after the necking breaks, the droplet starts to transfer in the arc space to the molten pool; in the next base value stage ①, the droplet in transfer contacts the molten pool and gradually wets and spreads, finally completing the droplet transfer process. However, titanium alloy has higher surface tension than iron alloy, aluminum alloy and other materials, which makes titanium alloy need larger current to achieve rapid and stable necking breaking process. If the traditional GMAW-P current waveform is directly used in titanium alloy welding, it will cause the problem of over-elongated necking, and then cause the phenomenon of slow droplet transfer speed. The droplet may not complete the transfer in the next base value stage ①, and finally generate severe welding spatter under the action of strong cathode jet.

[0048] According to the splash forming mechanism, the application provides a waveform control method for reducing the splash rate of titanium alloy GMAW-P welding, which improves the traditional GMAW-P current waveform by adding a separate pulse and prolonging the base value time, so that the current waveform is more suitable for the physical properties of titanium alloy, which has higher surface tension and strong cathode jet.

[0049] Figure 3 (b) The current waveform of the titanium alloy GMAW-P proposed by the application is divided into three stages: ① base value stage; ② main pulse stage; and ③ separate pulse stage. Compared with the traditional GMAW-P current waveform, the titanium alloy GMAW-P current waveform proposed by the application has two important characteristics: one is that a separate pulse is added, and the other is that the base value time is prolonged.

[0050] The addition of a separate pulse refers to outputting a separate pulse at the end of the main pulse to achieve a rapid and stable neck break process. In this way, the droplet can be given a larger transition speed than a single pulse, so that it can quickly fall into the molten pool and complete the transition in the next base value stage ①.

[0051] Prolonging the base value time refers to appropriately prolonging the time of the next base value stage ① according to the time required for the droplet to contact the molten pool from separation during splash formation, so that the droplet can smoothly complete the transition even if it has a slower transition speed.

[0052] The research on the titanium alloy GMAW-P droplet transfer of the application shows that it is more appropriate to set the separate pulse current to 50-80% of the main pulse current and the separate pulse time to 70-130% of the main pulse time. When the separate pulse current is less than 50% of the main pulse current or the separate pulse time is less than 70% of the main pulse time, the improvement effect of the droplet transition speed is not obvious; when the separate pulse current is greater than 80% of the main pulse current or the separate pulse time is greater than 130% of the main pulse time, the excessive droplet transition speed will cause the molten pool to be unstable when the droplet contacts the molten pool.

[0053] The research on the titanium alloy GMAW-P droplet transfer of the application shows that the time required for the droplet to contact the molten pool from separation during splash formation is about 10ms, so it is more appropriate to prolong the base value time to 11-15ms, and when the base value time is less than 11ms, the droplet may still be unable to complete the transition in the next base value stage ①, and when the base value time is greater than 15ms, the excessively long base value stage ① will cause difficulty in re-arc.

[0054] In addition, if only the separation pulse is added without prolonging the base value time, a separation pulse current greater than 80% or a separation pulse time greater than 130% is required to ensure the same splash suppression effect, but the excessive droplet transfer speed will cause the molten pool to be unstable. If only the base value time is prolonged without adding the separation pulse, a base value time greater than 15 ms is required to ensure the same splash suppression effect, but the excessively long base value time will cause difficulty in re-arc. Therefore, both the measures of adding the separation pulse and prolonging the base value time should be adopted at the same time to ensure better welding effect.

[0055] As a preferred embodiment, the welding is performed by using the waveform control method for reducing the splash rate of the GMAW-P welding of the titanium alloy according to the present application, and the specific implementation steps are as follows:

[0056] (1) On the basis of 40-60 A base value current, 300-400 A main pulse current, and 2-3 ms main pulse time, a separation pulse with a current of 50-80% of the main pulse current and a time of 70-130% of the main pulse time is added, and the base value time is prolonged to 11-15 ms.

[0057] (2) Before the test, the titanium alloy workpiece is polished using an angle grinder, and then the titanium alloy workpiece is placed in ethanol for ultrasonic cleaning. Appropriate welding speed and wire feeding speed are set, and TC4 welding wire and high-purity argon are used for welding.

[0058] (3) Start welding, and end welding after a period of time.

[0059] It can be seen that, in the GMAW-P of the titanium alloy, by adding the separation pulse and prolonging the base value time, and on this basis, the parameter range of the appropriate separation pulse current, separation pulse time and base value time is determined, the molten droplet can be prevented from being shot out under the action of the strong cathode jet when it contacts the molten pool, so that the welding splash rate is greatly reduced. In addition, the selected parameter range also needs to ensure that the molten pool is not unstable due to excessive transfer speed, and that the re-arc is not difficult due to the excessively long base value time.

[0060] In order to further understand the invention content, characteristics and effects of the present application, the following will be described in detail in combination with the embodiments and the drawings.

[0061] Example 1

[0062] The base current was set to 40 A, the main pulse current to 300 A, and the main pulse time to 2.0 ms. The separation pulse current was set to 240 A (80% of the main pulse current), the separation pulse time to 2.6 ms (130% of the main pulse time), and the base time to 15 ms. The titanium alloy workpiece was polished using an angle grinder 1 h before the test, and then the workpiece was ultrasonically cleaned in ethanol for 40 min. The welding speed was set to 0.30 m / min, and the wire feeding speed to 4.7 m / min. A TC4 welding wire with a diameter of 1.2 mm was used, and argon with a purity of 99.99% was used as the shielding gas at a flow rate of 18 L / min.

[0063] Example 2

[0064] The base current was set to 50 A, the main pulse current to 350 A, and the main pulse time to 2.5 ms. The separation pulse current was set to 231 A (66% of the main pulse current), the separation pulse time to 2.5 ms (100% of the main pulse time), and the base time to 13 ms. The titanium alloy workpiece was polished using an angle grinder 1 h before the test, and then the workpiece was ultrasonically cleaned in ethanol for 35 min. The welding speed was set to 0.33 m / min, and the wire feeding speed to 5.3 m / min. A TC4 welding wire with a diameter of 1.2 mm was used, and argon with a purity of 99.99% was used as the shielding gas at a flow rate of 20 L / min.

[0065] Example 3

[0066] The base current was set to 60 A, the main pulse current to 400 A, and the main pulse time to 3.0 ms. The separation pulse current was set to 200 A (50% of the main pulse current), the separation pulse time to 2.1 ms (70% of the main pulse time), and the base time to 11 ms. The titanium alloy workpiece was polished using an angle grinder 1 h before the test, and then the workpiece was ultrasonically cleaned in ethanol for 45 min. The welding speed was set to 0.36 m / min, and the wire feeding speed to 5.9 m / min. A TC4 welding wire with a diameter of 1.2 mm was used, and argon with a purity of 99.99% was used as the shielding gas at a flow rate of 19 L / min.

[0067] Example 4

[0068] The base current was set to 40 A, the main pulse current to 300 A, and the main pulse time to 2.0 ms. The separation pulse current was set to 210 A (70% of the main pulse current), the separation pulse time to 2.2 ms (110% of the main pulse time), and the base time to 14 ms. The titanium alloy workpiece was polished using an angle grinder 1 h before the test, and then the workpiece was ultrasonically cleaned in ethanol for 50 min. The welding speed was set to 0.27 m / min, and the wire feeding speed to 4.1 m / min. A TC4 welding wire with a diameter of 1.2 mm was used, and argon with a purity of 99.99% was used as the shielding gas at a flow rate of 17 L / min.

[0069] Figure 4 and Figure 5 The control effects of Examples 1-4 are demonstrated:

[0070] observe Figure 4 It can be seen that, with Figure 1 In contrast, after waveform control, the molten droplets are not subjected to strong cathode jets during the transition in the arc space, which significantly suppresses the chaotic droplet transition behavior that leads to spatter formation.

[0071] observe Figure 5 It can be seen that, with Figure 2 In comparison, after waveform control, the number of splash particles on the workpiece surface was significantly reduced, and the splash rate was greatly reduced from 13.67% to 1-3%.

[0072] It is evident that the waveform control method proposed in this invention can effectively reduce the spatter rate in the titanium alloy GMAW-P process.

[0073] Although the preferred embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many specific modifications under the guidance of the present invention without departing from the spirit and scope of the claims, and these modifications all fall within the scope of protection of the present invention.

Claims

1. A waveform control method for reducing GMAW-P spatter rate of a titanium alloy, characterized by, The traditional GMAW-P current waveform is improved by adding a separate pulse and prolonging the base value time, so that the titanium alloy GMAW-P current waveform is divided into three stages: base value stage, main pulse stage and separate pulse stage. The separate pulse is output at the same time as the end of the main pulse to realize a rapid and stable neck fracture process, thereby increasing the droplet transfer speed and making the droplet quickly fall into the molten pool and complete the transfer in the next base value stage. The base value time is prolonged according to the time required for the droplet to separate from the molten pool to contact the molten pool when spatter is formed, so that the droplet smoothly completes the transfer in the prolonged next base value stage.

2. The waveform control method of reducing GMAW-P spatter of a titanium alloy according to claim 1, characterized by, The traditional GMAW-P current waveform is divided into two stages: base value stage and pulse stage; the pulse stage is equivalent to the main pulse stage in the titanium alloy GMAW-P current waveform.

3. The waveform control method of reducing GMAW-P spatter of a titanium alloy according to claim 1, characterized by, The current of the separate pulse is set to 50-80% of the main pulse current, and the time of the separate pulse is set to 70-130% of the main pulse time.

4. The waveform control method of reducing spatter rate of GMAW-P welding of titanium alloy according to claim 1, characterized in that, The prolonged base value time is 11-15 ms.

5. The waveform control method of reducing spatter rate of GMAW-P welding of titanium alloy according to claim 1, characterized in that, On the basis of a base value current of 40-60 A, a main pulse current of 300-400 A and a main pulse time of 2-3 ms, a separate pulse with a current of 50-80% of the main pulse current and a time of 70-130% of the main pulse time is added, and the base value time is prolonged to 11-15 ms.

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