A MIG welding method for high-pressure aluminum die castings and profiles

Abstract

The present invention provides a MIG welding method for high-pressure aluminum die castings and profiles, and relates to the field of welding technology. The present invention adopts a direct current pulse current for welding in the arc starting stage, and adopts a relatively high welding current, so as to increase the heat input in the arc starting stage, and ensure that the molten pool can be formed quickly; after the arc starting is completed, on the basis of reducing the welding current, the direct current pulse current is gradually switched to a variable polarity pulse current, and the time proportion of the negative polarity stage in the welding current waveform is gradually increased, which is conducive to improving the melting speed of the welding wire during the welding process, thereby increasing the amount of welding wire filling in the weld bead, and at the same time, it is conducive to reducing the heat accumulation during the welding process, and can effectively inhibit the generation of pores in the molten pool, so as to reduce the pore defects in the welding sample. In addition, the welding current is gradually reduced before the arc closing stage, and the arc closing is carried out by using a variable polarity short circuit, which is conducive to ensuring that the arc pit is full during welding, and is also conducive to reducing the pore defects in the welding sample.

Description

Technical Field

[0001] The invention relates to the technical field of welding, and in particular to a MIG welding method for high-pressure aluminum die castings and profiles. Background Art

[0002] ‌High-pressure aluminum die castings are aluminum alloy products produced by high-pressure die casting process. They are lightweight, corrosion-resistant, and high-strength, and are widely used in the automotive manufacturing industry and other fields. High-pressure aluminum die castings and aluminum profile MIG welding is one of the most cost-effective and accessible methods in all aluminum alloy connection processes. In the existing MIG welding process of high-pressure aluminum die castings and profiles, a DC MIG welding method is generally used, that is, a DC pulse and short-circuit mixed method is used, a high pulse of a constant frequency is used to generate high heat to melt the parent material to open the molten pool, a low pulse of a constant frequency or a short circuit of a constant frequency is used to provide welding wire filling material and cool the molten pool, so as to achieve continuous and stable welding of the weld. The characteristics of this process are large heat input and alternating cooling during welding, which is suitable for aluminum alloy welding; this process has the following disadvantages: large heat input during welding. When welding high-pressure aluminum die castings and profiles, since the melting temperature of high-pressure aluminum die castings is generally 450-650°C, and the melting temperature of aluminum profiles is generally 660-750°C, the melting point of high-pressure aluminum die castings is relatively low, resulting in a large amount of molten casting material in the welding molten pool, and a large amount of pores in the castings will overflow into the welding molten pool, forming pore defects on the welding surface and internal pore defects. When a large amount of gas floats out of the welding surface inside the aluminum die casting, the overflowing gas will destroy the protective gas atmosphere, causing a large amount of slag to form on the surface of the sample, resulting in blackening of the weld surface, and the weld being unformed. During the welding process, the proportion of welding wire in the weld is usually increased by increasing the amount of welding wire melted, thereby reducing the porosity of the weld. However, as the welding wire feed speed increases, the heat input in DC MIG welding will continue to increase. The increased heat input will greatly increase the melted pores in the weld. Summary of the invention

[0003] The problem solved by the invention is: how to reduce the porosity defects of welding samples when performing MIG welding of high-pressure aluminum die castings and profiles.

[0004] In order to solve the above problems, the present invention provides a MIG welding method for high-pressure aluminum die castings and profiles, comprising:

[0005] Step S1, arc starting stage: the welding current adopts a DC pulse current; the polarity of the welding current in the arc starting stage is positive polarity, and the average welding current in the arc starting stage is I1;

[0006] Step S2, first transition stage: keep the waveform of the welding current consistent with the arc starting stage, only make the amplitude of the welding current waveform gradually decay until the average welding current of the last decay cycle is I2, and then enter the variable polarity transition stage; the welding current waveform of the last decay cycle is the first waveform, and the variable polarity transition stage includes multiple transition cycles, wherein the welding current waveform of the first transition cycle is obtained by switching the polarity of a part of the bands in the first waveform to negative polarity, and gradually increase the time proportion of the negative polarity stage in the welding current waveform of the subsequent transition cycle to obtain the welding current waveform of the subsequent transition cycle; the time proportion of the negative polarity stage in the last transition cycle is a first preset value;

[0007] Step S3, main welding stage: the welding current adopts a variable polarity pulse current; the welding current waveform of the last transition cycle is the second waveform, and the main welding stage includes multiple variable polarity cycles, wherein the welding current waveform of the first variable polarity cycle is obtained by further increasing the time proportion of the negative polarity stage in the second waveform, and gradually increasing the time proportion of the negative polarity stage in the welding current waveform of the subsequent variable polarity cycle to obtain the welding current waveform of the subsequent variable polarity cycle; the time proportion of the negative polarity stage in the last variable polarity cycle is the second preset value;

[0008] Step S4, arc closure stage: keep the waveform of the welding current consistent with the last polarity change cycle, and only make the amplitude of the waveform of the welding current gradually decay until the average welding current of the last decay cycle is I3, and then adopt polarity change short circuit to extinguish the arc;

[0009] Among them, the ratio of I1, I3 and I2 is (1.25-1.35): (0.25-0.35):1.

[0010] Optionally, in step S2, the first preset value is 14-16%.

[0011] Optionally, in step S3, the second preset value is 20-30%.

[0012] Optionally, in step S2, the process of gradually attenuating the amplitude of the welding current waveform takes 0.4-0.6 s.

[0013] Optionally, in step S2, the polarity change transition phase takes 0.4-0.6 s.

[0014] Optionally, in step S4, the process of gradually attenuating the amplitude of the welding current waveform takes 0.4-0.6 s.

[0015] Optionally, in step S4, the arc extinguishing by changing polarity short circuit takes 0.5-0.8s.

[0016] Optionally, in step S1, the arc starting stage includes multiple DC pulse cycles, wherein each DC pulse cycle includes an initial stage, a current increase stage, a holding stage, a current reduction stage and a final stage, the welding current in the initial stage is 30A, and the holding time is 2ms; the welding current in the current increase stage increases from 30A to 550A after 0.2ms; the welding current in the holding stage is 550A, and the holding time is 2ms; the welding current in the current reduction stage decreases from 550A to 30A after 0.2ms, and the welding current in the final stage is 30A, and the holding time is 2ms.

[0017] Optionally, in step S3, the welding speed in the main welding stage is 0.8-1.0 m / min.

[0018] Optionally, the material of the high-pressure aluminum die casting is ALSi10MgMn, and the material of the profile is one of 6061 aluminum alloy, 6060 aluminum alloy, 6082 aluminum alloy and 6063 aluminum alloy.

[0019] Compared with the prior art, the present invention adopts a DC pulse current for welding in the arc starting stage, and adopts a relatively high welding current, so as to increase the heat input in the arc starting stage and ensure that the molten pool can be formed quickly; after the arc starting stage is completed, on the basis of reducing the welding current, the DC pulse current is gradually switched to a variable polarity pulse current, and the time proportion of the negative polarity stage in the welding current waveform is gradually increased. As the time proportion of the negative polarity stage in the welding current waveform increases, it is beneficial to increase the melting speed of the welding wire during the welding process, thereby increasing the amount of welding wire filling in the weld, and at the same time, it is beneficial to reduce the heat accumulation during the welding process, and can effectively inhibit the generation of pores in the molten pool, so as to reduce the pore defects in the welding sample. In addition, gradually reducing the welding current before the arc closing stage and adopting a variable polarity short circuit to close the arc are beneficial to ensure that the arc pit is full during welding, and are also beneficial to reduce the pore defects in the welding sample. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the waveform of the DC pulse current used in the arc starting stage in an embodiment of the present invention;

[0021] Figure 2 Schematic diagram of welding current waveform in the last transition period in an embodiment of the present invention;

[0022] Figure 3 Schematic diagram of welding current waveform in the last polarity changing cycle in an embodiment of the present invention;

[0023] Figure 4 Graph showing the temperature distribution of the weld bead back during the main welding phase in Example 1;

[0024] Figure 5 This is a diagram showing the temperature distribution on the back of the weld in the main welding stage in Comparative Example 1. DETAILED DESCRIPTION

[0025] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. Although certain embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be interpreted as being limited to the embodiments described herein. On the contrary, these embodiments are provided to provide a more thorough and complete understanding of the present invention. It should be understood that the drawings and embodiments of the present invention are only for exemplary purposes and are not intended to limit the scope of protection of the present invention.

[0026] Unless otherwise defined, all technical and scientific terms used in this application have the same meanings as those commonly understood by those skilled in the art to which this application belongs; the terms used in the specification of this application are only for the purpose of describing specific implementation methods and are not intended to limit this application;

[0027] The term "including" and its variations used in this article are open inclusions, that is, "including but not limited to"; the term "based on" means "at least partially based on"; the term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one other embodiment"; the term "some embodiments" means "at least some embodiments"; the term "optionally" means "optional embodiments". The relevant definitions of other terms will be given in the following description. It should be noted that the concepts of "first" and "second" mentioned in the present invention are used to distinguish different objects, rather than to describe a specific order or a primary and secondary relationship. In addition, the terms "first" and "second" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of this application, unless otherwise specified, "multiple" means two or more. It should be noted that, Figure 1-3 Here I represents welding current and t represents time.

[0028] An embodiment of the present invention provides a MIG welding method for high-pressure aluminum die castings and profiles, comprising:

[0029] Step S1, arc starting stage: the welding current adopts a DC pulse current; the polarity of the welding current in the arc starting stage is positive polarity, and the average welding current in the arc starting stage is I1; illustratively, the waveform of the DC pulse current is as follows: Figure 1 As shown;

[0030] Step S2, first transition stage: keep the waveform of the welding current consistent with the arc starting stage, only make the amplitude of the welding current waveform gradually decay until the average welding current of the last decay cycle is I2, and then enter the variable polarity transition stage; the welding current waveform of the last decay cycle is the first waveform, and the variable polarity transition stage includes multiple transition cycles, wherein the welding current waveform of the first transition cycle is obtained by switching the polarity of a part of the bands in the first waveform to negative polarity, and gradually increase the time proportion of the negative polarity stage in the welding current waveform of the subsequent transition cycle to obtain the welding current waveform of the subsequent transition cycle; the time proportion of the negative polarity stage in the last transition cycle is a first preset value;

[0031] Step S3, main welding stage: the welding current adopts variable polarity pulse current; Figure 2 As shown, the welding current waveform of the last transition cycle is the second waveform, and the main welding stage includes multiple polarity change cycles, wherein the welding current waveform of the first polarity change cycle is obtained by further increasing the time proportion of the negative polarity stage in the second waveform, and gradually increasing the time proportion of the negative polarity stage in the welding current waveform of the subsequent polarity change cycle to obtain the welding current waveform of the subsequent polarity change cycle; the time proportion of the negative polarity stage in the last polarity change cycle is the second preset value; for example, the welding current waveform of the last polarity change cycle is as follows Figure 3 shown.

[0032] Step S4, arc closure stage: keep the waveform of the welding current consistent with the last polarity change cycle, and only make the amplitude of the waveform of the welding current gradually decay until the average welding current of the last decay cycle is I3, and then adopt polarity change short circuit to extinguish the arc;

[0033] Among them, the ratio of I1, I3 and I2 is (1.25-1.35): (0.25-0.35):1.

[0034] The embodiment of the present invention adopts a DC pulse current for welding in the arc starting stage, and adopts a relatively high welding current, so as to increase the heat input in the arc starting stage and ensure that the molten pool can be formed quickly; after the arc starting stage is completed, on the basis of reducing the welding current, the DC pulse current is gradually switched to a variable polarity pulse current, and the time proportion of the negative polarity stage in the welding current waveform is gradually increased. As the time proportion of the negative polarity stage in the welding current waveform increases, it is beneficial to increase the melting speed of the welding wire during the welding process, thereby increasing the amount of welding wire filling in the weld, and at the same time, it is beneficial to reduce the heat accumulation during the welding process, and can effectively inhibit the generation of pores in the molten pool, so as to reduce the pore defects in the welding sample. In addition, gradually reducing the welding current before the arc closing stage and adopting a variable polarity short circuit to close the arc is beneficial to ensure that the arc pit is full during welding, and is also beneficial to reduce the pore defects in the welding sample.

[0035] It should be noted that I2 is related to the thickness h of the high-pressure aluminum die casting and can be calculated by the following formula:

[0036] I2=64.8h-2.43h²+1;

[0037] The unit of h in the above formula is mm.

[0038] In some embodiments of the present invention, in step S2, the first preset value is 14-16%.

[0039] In some embodiments of the present invention, in step S3, the second preset value is 20-30%.

[0040] In some embodiments of the present invention, in step S2, the process of gradually attenuating the amplitude of the waveform of the welding current takes 0.4-0.6 s.

[0041] In some embodiments of the present invention, in step S2, the polarity change transition phase takes 0.4-0.6 s.

[0042] In some embodiments of the present invention, in step S4, the process of gradually attenuating the amplitude of the waveform of the welding current takes 0.4-0.6 s.

[0043] In some embodiments of the present invention, in step S4, the arc extinguishing by using a polarity-changing short circuit takes 0.5-0.8 s.

[0044] In some embodiments of the present invention, in step S1, the arc starting stage includes a plurality of DC pulse cycles, wherein: Figure 1 As shown, each DC pulse cycle includes an initial stage, a current increasing stage, a holding stage, a current reducing stage and a final stage. The welding current in the initial stage is 30A, and the holding time is 2ms; the welding current in the current increasing stage increases from 30A to 550A after 0.2ms; the welding current in the holding stage is 550A, and the holding time is 2ms; the welding current in the current reducing stage decreases from 550A to 30A after 0.2ms, and the welding current in the final stage is 30A, and the holding time is 2ms.

[0045] In some embodiments of the present invention, in step S3, the welding speed of the main welding stage is 0.8-1.0 m / min.

[0046] In some embodiments of the present invention, exemplarily, the material of the high pressure aluminum die casting is ALSi10MgMn, and the material of the profile is one of 6061 aluminum alloy, 6060 aluminum alloy, 6082 aluminum alloy and 6063 aluminum alloy.

[0047] The present invention is further described below in conjunction with specific embodiments.

[0048] Embodiment 1: A high-pressure aluminum die-casting and a profile are welded. The material of the high-pressure aluminum die-casting is ALSi10MgMn with a thickness of 10 mm, and the material of the profile is 6061 aluminum alloy.

[0049] A1, arc starting stage: the welding current adopts a DC pulse current; the polarity of the welding current in the arc starting stage is positive polarity, and the average welding current in the arc starting stage is I1;

[0050] A2, first transition stage: keep the waveform of welding current consistent with the arc starting stage, only make the amplitude of welding current waveform gradually decay, until the average welding current of the last decay cycle is I2, then enter the variable polarity transition stage; the welding current waveform of the last decay cycle is the first waveform, the variable polarity transition stage includes multiple transition cycles, wherein the welding current waveform of the first transition cycle is obtained by switching the polarity of a part of the band in the first waveform to negative polarity, gradually increase the time proportion of negative polarity stage in the welding current waveform of subsequent transition cycles, and obtain the welding current waveform of subsequent transition cycles; the time proportion of negative polarity stage in the last transition cycle is 15%;

[0051] A3, main welding stage: the welding current adopts variable polarity pulse current; the welding current waveform of the last transition cycle is the second waveform, and the main welding stage includes multiple variable polarity cycles, wherein the welding current waveform of the first variable polarity cycle is obtained by further increasing the time proportion of the negative polarity stage in the second waveform, and gradually increasing the time proportion of the negative polarity stage in the welding current waveform of the subsequent variable polarity cycle to obtain the welding current waveform of the subsequent variable polarity cycle; the time proportion of the negative polarity stage in the last variable polarity cycle is 20%;

[0052] A4, arc closure stage: keep the waveform of the welding current consistent with the last polarity change cycle, and only make the amplitude of the welding current waveform gradually decay until the average welding current of the last decay cycle is I3, and then adopt polarity change short circuit to extinguish the arc, and obtain the welding sample;

[0053] Among them, the ratio of I1, I3 and I2 is 1.3:0.3:1.

[0054] Example 2

[0055] The difference from Example 1 is that in step A3, the negative polarity phase in the last polarity change cycle accounts for 25% of the time.

[0056] Example 3

[0057] The difference from Example 1 is that in step A3, the time of the negative polarity stage in the last polarity change cycle accounts for 30%.

[0058] Comparative Example 1: A high-pressure aluminum die-casting and a profile are welded. The material of the high-pressure aluminum die-casting is ALSi10MgMn with a thickness of 10 mm, and the material of the profile is 6061 aluminum alloy.

[0059] A1, arc starting stage: the welding current adopts a DC pulse current; the polarity of the welding current in the arc starting stage is positive polarity, and the average welding current in the arc starting stage is I1;

[0060] A2, the first transition stage: keep the waveform of the welding current consistent with the arc starting stage, and only gradually decay the amplitude of the welding current waveform until the average welding current of the last decay cycle is I2;

[0061] A3. Main welding stage: In this stage, direct current pulse current is used for welding, and the waveform of the welding current is consistent with the last attenuation cycle.

[0062] A4, arc closure stage: keep the waveform of the welding current consistent with the last decay cycle, and only make the amplitude of the waveform of the welding current gradually decay until the average welding current of the last decay cycle is I3, and then use polarity-changing short circuit to extinguish the arc to obtain a welding sample;

[0063] Among them, the ratio of I1, I3 and I2 is 1.3:0.3:1.

[0064] Comparative Example 2: A high-pressure aluminum die-casting and a profile are welded. The material of the high-pressure aluminum die-casting is ALSi10MgMn with a thickness of 10 mm, and the material of the profile is 6061 aluminum alloy.

[0065] A1, arc starting stage: the welding current adopts a DC pulse current; the polarity of the welding current in the arc starting stage is positive polarity, and the average welding current in the arc starting stage is I1;

[0066] A2, first transition stage: keep the waveform of the welding current consistent with that of the arc starting stage, and only gradually decay the amplitude of the welding current waveform until the average welding current of the last decay cycle is I2, and the welding current waveform of the last decay cycle is the first waveform;

[0067] A3, main welding stage: the welding current adopts variable polarity pulse current; the main welding stage includes a plurality of variable polarity cycles, wherein the welding current waveform of each variable polarity cycle is obtained by switching the polarity of a part of the band in the first waveform to negative polarity, and the time proportion of the negative polarity stage in each variable polarity cycle is 20%;

[0068] A4, arc closure stage: keep the waveform of the welding current consistent with the polarity change cycle, and only make the amplitude of the welding current waveform gradually decay until the average welding current of the last decay cycle is I3, and then adopt polarity change short circuit to closure; obtain welding samples;

[0069] Among them, the ratio of I1, I3 and I2 is 1.3:0.3:1.

[0070] Experimental example

[0071] The temperature of the back of the weld in the main welding stage in Example 1 and Comparative Example 1 was tested, and the results are shown in Figure 4 and Figure 5 ,from Figure 4 It can be seen that the temperature of the back of the weld bead in the main welding stage in Example 1 is about 240°C, and the temperature of the back of the weld bead in the main welding stage in Comparative Example 1 is about 300°C.

[0072] The porosity and average pore size of the welding samples prepared in Examples 1-3 and Comparative Examples 1-2 were tested, and the results are shown in Table 1. It can be seen from Table 1 that, compared with the comparative examples, the porosity of the welding samples prepared in Examples 1-3 is smaller, and the average pore size of the pores is smaller.

[0073] Table 1

[0074]

[0075] Although the present invention is disclosed as above, the protection scope of the present invention is not limited thereto. Those skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention, and these changes and modifications will fall within the protection scope of the present invention.

Claims

1. A MIG welding method for high pressure aluminum die castings and aluminum profiles, characterized in that: include: Step S1, arc starting stage: the welding current adopts a DC pulse current; The polarity of the welding current in the arc starting stage is positive polarity, and the average welding current in the arc starting stage is I1; Step S2, first transition stage: keep the waveform of the welding current consistent with the arc starting stage, only make the amplitude of the welding current waveform gradually decay until the average welding current of the last decay cycle is I2, and then enter the variable polarity transition stage; the welding current waveform of the last decay cycle is the first waveform, and the variable polarity transition stage includes multiple transition cycles, wherein the welding current waveform of the first transition cycle is obtained by switching the polarity of a part of the bands in the first waveform to negative polarity, and gradually increase the time proportion of the negative polarity stage in the welding current waveform of the subsequent transition cycle to obtain the welding current waveform of the subsequent transition cycle; the time proportion of the negative polarity stage in the last transition cycle is a first preset value; Step S3, main welding stage: the welding current adopts a variable polarity pulse current; the welding current waveform of the last transition cycle is the second waveform, and the main welding stage includes multiple variable polarity cycles, wherein the welding current waveform of the first variable polarity cycle is obtained by further increasing the time proportion of the negative polarity stage in the second waveform, and gradually increasing the time proportion of the negative polarity stage in the welding current waveform of the subsequent variable polarity cycle to obtain the welding current waveform of the subsequent variable polarity cycle; the time proportion of the negative polarity stage in the last variable polarity cycle is the second preset value; Step S4, arc closure stage: keep the waveform of the welding current consistent with the last polarity change cycle, and only make the amplitude of the waveform of the welding current gradually decay until the average welding current of the last decay cycle is I3, and then adopt polarity change short circuit to extinguish the arc; Among them, the ratio of I1, I3 and I2 is (1.25-1.35): (0.25-0.35):

1.

2. The MIG welding method for high pressure aluminum die casting and aluminum profile according to claim 1, characterized in that: In step S2, the first preset value is 14-16%.

3. The MIG welding method for high pressure aluminum die casting and aluminum profile according to claim 1, characterized in that: In step S3, the second preset value is 20-30%.

4. The MIG welding method for high pressure aluminum die casting and aluminum profile according to claim 1, characterized in that: In step S2, the process of gradually attenuating the amplitude of the welding current waveform takes 0.4-0.6 s.

5. The MIG welding method for high pressure aluminum die casting and aluminum profile according to claim 1, characterized in that: In step S2, the polarity change transition phase takes 0.4-0.6 s.

6. The MIG welding method for high pressure aluminum die casting and aluminum profile according to claim 1, characterized in that: In step S4, the process of gradually attenuating the amplitude of the welding current waveform takes 0.4-0.6 seconds.

7. The MIG welding method for high pressure aluminum die casting and aluminum profile according to claim 1, characterized in that: In the step S4, the arc extinguishing by changing polarity and short-circuiting takes 0.5-0.8s.

8. The MIG welding method for high pressure aluminum die casting and aluminum profile according to claim 1, characterized in that: In step S1, the arc starting stage includes multiple DC pulse cycles, wherein each DC pulse cycle includes an initial stage, a current increase stage, a holding stage, a current reduction stage and a final stage, the welding current in the initial stage is 30A, and the holding time is 2ms; the welding current in the current increase stage increases from 30A to 550A after 0.2ms; the welding current in the holding stage is 550A, and the holding time is 2ms; the welding current in the current reduction stage decreases from 550A to 30A after 0.2ms, and the welding current in the final stage is 30A, and the holding time is 2ms.

9. The MIG welding method for high pressure aluminum die casting and aluminum profile according to claim 1, characterized in that: In the step S3, the welding speed in the main welding stage is 0.8-1.0 m / min.

10. The MIG welding method for high pressure aluminum die casting and aluminum profile according to any one of claims 1 to 9, characterized in that: The material of the high-pressure aluminum die casting is ALSi10MgMn, and the material of the aluminum profile is one of 6061 aluminum alloy, 6060 aluminum alloy, 6082 aluminum alloy and 6063 aluminum alloy.

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