CN100584504C - Sub-jet transition adaptive control method for aluminum and aluminum alloy metal arc welding - Google Patents

Abstract

The invention relates to material processing technology and welding. Specifically, the invention relates to a sub-jet transition adaptive control method for gas shielded welding of aluminum and aluminum alloys. In order to provide a sub-jet transition adaptive control method for gas shielded welding of aluminum and aluminum alloys, control the welding arc length, and solve some major technical problems in the welding of aluminum and aluminum alloys, such as pores, cracks, pinching Defects such as slag, as well as problems such as weld formation and coarse grains, the technical solution adopted in the present invention is: the sub-jet transition adaptive control method of aluminum and aluminum alloy gas shielded welding, comprising the following steps: selecting the slope of the ab line greater than or equal to the slope of the static characteristic of the arc passing through point a, the slope of line ed should be greater than or equal to the slope of the static characteristic of arc passing through point d, line ae and line cd are two constant current characteristic curves of the power supply, and the slope of line bc should be Obviously greater than the slope of the iso-melting curve; make the arc burn on the ae line, when the arc voltage is less than or equal to the voltage at point a, make the arc current jump to point b and increase along the bc line, and the arc burns stably on the cd line, when the arc voltage When it is greater than or equal to the voltage value of a certain point on the cd line, the arc current jumps to the ae line for combustion and enters the next cycle. The invention is mainly used in material processing technology and welding.

Description

Sub-jet transition adaptive control method for aluminum and aluminum alloy metal arc welding

technical field

The invention relates to material processing technology and welding. Specifically, the invention relates to a sub-jet transition adaptive control method for gas shielded welding of aluminum and aluminum alloys.

Background technique

The droplet transfer methods of aluminum MIG welding include large droplet transfer, jet droplet transfer, short-circuit transfer and sub-shot droplet transfer. The large droplet transfer is the droplet transfer mode when the current is small; when the current exceeds the critical current of the droplet transfer, the droplet transfer mode becomes the droplet transfer. At this time, the diameter of the droplet is close to the diameter of the welding wire, and the droplet transitions away from the welding wire along the axial direction, and the acceleration is greater than the acceleration of gravity.

For DC welding of aluminum and aluminum alloy MIG welding (i.e. molten electrode gas shielded welding), the droplet transfer method is generally used, which is suitable for welding requirements of medium and thick plates or large current capacity. When it is necessary to reduce the welding current capacity, the method of pulse current welding is often used at present, instead of the large droplet transfer and short-circuit transfer methods, because the quality of the weld seam is not good in this droplet transfer method.

There are many types of pulse current MIG welding methods for aluminum and aluminum alloys, such as: pulse MIG welding of thin-plate aluminum alloys controlled by the power supply with vertical and external drag characteristics, double pulse MIG welding, AC pulse MIG welding, adaptive closed-loop control of arc length method, Synergic control with automatic arc length balancing for wire feed speed fluctuations, etc. However, there is no literature report on specifically controlling the arc and droplet transfer in the sub-jet transfer zone.

Sub-jet transfer is customarily called sub-jet transfer, and it is a droplet transfer method between droplet transfer and short-circuit transfer. Its arc length is relatively short, generally ranging from 2 to 8mm. Under the action of arc heat, the droplet grows up and short-circuits with the molten pool when the neck is formed and is about to separate from the welding wire in a droplet manner. The thin neck is broken under the action of electromagnetic contraction force, and the arc is re-ignited to complete the transition. The droplet short-circuit time of the sub-jet transition is extremely short, the current rises little, the necking breaks, and the existence area is very narrow, as shown in Figure 1. The characteristics of the current and voltage values that produce the sub-jet transition are: the current generally exceeds the critical current of the droplet transition, and the voltage cannot be too high.

The use of sub-jet arc welding of aluminum and aluminum alloys has some characteristics different from other welding methods. (1) Advantages: (a) The arc is dish-shaped, the cathode atomization area is large, the phenomenon of weld wrinkling and surface black powder is less than that of jet flow; (b) constant current external characteristic power supply can be used for welding; (c) jet arc The penetration shape is "finger-shaped", while the sub-jet arc is "bowl-shaped", which avoids defects such as insufficient penetration caused by "finger-shaped" penetration. (2) Disadvantages: The arc length range of the sub-jet arc is not wide (φ1.6 aluminum welding wire 2~8mm). For a certain wire feeding speed, the optimal welding current range is quite narrow and difficult to control.

The arc length of the sub-jet transition arc is relatively short, and it expands into a dish shape around it. There are also different characteristics in melting characteristics. Figure 2 is the melting characteristic curve of φ1.6 aluminum welding wire [data from E. Halmoy's research paper Electrode melting in arc welding, Physical aspects of arc welding, 81~93, IIW Group212, 1993.9], also known as isomelting curve. Each curve represents a wire feed speed, and the numbers on the characteristic curve represent the distance between the end of the welding wire and the surface of the base metal (ie, the visible length of the arc). It can be seen from the figure that the melting characteristic curve of the welding wire is almost a vertical line in the droplet transition area, and the melting coefficient of the welding wire is basically not affected by the arc length. However, after entering the sub-jet transition zone, the characteristic curve bends to the left, and the melting coefficient decreases with the increase of the arc length, and increases with the decrease of the arc length. And this change is more obvious under high current. If the arc length is further reduced (below about 2mm), the characteristic curve will bend to the right again, and the welding wire and the workpiece will be frequently short-circuited and enter the short-circuit transition zone. The melting of aluminum alloy welding wire also presents similar characteristics. Although the characteristic curve in Figure 2 is for φ1.6 aluminum welding wire, other aluminum and aluminum alloy welding wires with diameters ranging from φ0.8 to 2.4 also have similar characteristic curves.

To sum up, at present, there are some major technical problems in the welding of aluminum and aluminum alloys, such as defects such as pores, cracks, and slag inclusions, as well as problems such as weld formation and coarse grains.

The interval of sub-jet transition is very narrow, the arc length is short, and it is difficult to control. If the control arc length is short, the arc length fluctuates slightly, and it is easy to enter the short-circuit transition zone; if the control arc length is longer, it is easy to enter the droplet transition zone. Moreover, the control of the arc length is mainly carried out by detecting the arc voltage, and the change of the arc voltage caused by the change of the arc length in the sub-jet transition zone is small, and the change range is very narrow, and the smaller the current, the greater the range of the arc voltage change. narrower.

Contents of the invention

In order to overcome the deficiencies in the prior art, the object of the present invention is to provide a sub-jet transition adaptive control method for gas shielded welding of aluminum and aluminum alloys, control the welding arc length, and solve some problems in the welding of aluminum and aluminum alloys. Larger technical problems, such as defects such as pores, cracks, and slag inclusions, as well as problems such as weld formation and coarse grains.

The technical scheme adopted in the present invention is: the sub-jet flow transition adaptive control method of aluminum and aluminum alloy gas shielded welding, comprising the following steps:

Determine the five points a, b, c, d and e: select the slope of line ab to be greater than or equal to the slope of the arc static characteristic passing through point a, the slope of line ed should be greater than or equal to the slope of the arc static characteristic passing through point d, a The voltage at point 14-19 volts, the voltage at point d is 20-30 volts, the voltage at point c is less than 5 volts at point d, the lines ae and cd are two constant current characteristic curves of the power supply, and the slope of line bc should be significantly greater than that of the iso-melting curve slope;

Make the arc burn on the ae line, and the arc voltage gradually decreases. When the arc voltage is less than or equal to the voltage at point a, the arc current jumps to point b and increases along the bc line, and the arc current on the cd line is constant, so that the arc is on the cd line Stable combustion, the voltage gradually increases, when the arc voltage is greater than or equal to the voltage value of a certain point on the cd line, the arc current jumps to the ae line to burn, and enters the next cycle.

The constant current value of the ae line is a base value current, which is less than 50 amperes.

The constant current value of the ae line is the base value current, which is selected as 30 amperes.

The constant current value of the cd line is a pulse current, greater than 180 amperes.

The constant current value of the cd line is a pulse current, which is selected as 235 amperes.

When the arc current frequently jumps between points a and d, the frequency of the pulse current increases automatically.

The difference between the voltage values at point a and point d determines the allowable arc length fluctuation range. When the allowable arc length fluctuation range is small, the arc current will frequently jump between points a and d, making the frequency of the pulse current Automatically increases with arc current jump.

The constant current of the cd line is a pulse current, and with the change of the arc voltage, the time of working in the pulse current is automatically adjusted to increase (or decrease).

The diameter of the welding wire used is between Φ0.8 and Φ2.4.

The present invention has the following effects: due to the selection of the five points a, b, c, d and e and the connection line of the present invention, the welding voltage and current are limited to the sub-jet transition zone, so the present invention strictly controls the welding arc length to sub-jet In the interval of jet transition, some major technical problems in the welding of aluminum and aluminum alloys have been solved, such as defects such as pores, cracks, slag inclusions, weld formation, and coarse grains.

Description of drawings

Figure 1 Distribution of droplet transfer form in aluminum MIG welding

Figure 2 Melting characteristics of aluminum MIG welding

Figure 3 Control of subjet arc

Figure 4 Al pulsed MIG welding adaptive control experiment waveform 1

Figure 5 Al pulsed MIG welding adaptive control experiment waveform 2

Fig. 6 High-speed camera 3 (1000 frame/s, φ1.6) of pulsed MIG welding adaptive control process

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and examples.

The interval of sub-jet transition is very narrow, the arc length is short, and it is difficult to control. If the control arc length is short, the arc length fluctuates slightly, and it is easy to enter the short-circuit transition zone; if the control arc length is longer, it is easy to enter the droplet transition zone. Moreover, the control of the arc length is mainly carried out by detecting the arc voltage, and the change of the arc voltage caused by the change of the arc length in the sub-jet transition zone is small, and the change range is very narrow, and the smaller the current, the greater the range of the arc voltage change. narrower.

In order to overcome the above shortcomings, the pulse current adaptive control mode shown in Figure 3 is adopted. The dotted line in the figure represents the iso-melting curve of aluminum MIG welding in Figure 2, and the area between the corresponding ab line and ed line is in the sub-jet transition zone; the mn line represents the static characteristics of the aluminum MIG welding arc, which is in the rising section of the U-shaped curve Line ae and line cd represent two constant current characteristic curves of power supply, the current of line ae is very small, it is difficult to form droplet transfer with such current, the current of line cd is relatively large, located in the jet transition area, enough to produce droplet transfer; line bc The slope should be greater than the slope of the melting curve such as the subjet transition zone.

The control process shown in Figure 3 is as follows: first, assume that the arc burns on the line ae, and the voltage gradually decreases. When the arc voltage is less than or equal to the voltage at point a, the current jumps to point b and increases along the line bc, and the arc current stabilizes at line cd Combustion; the arc burns stably on the cd line, and the voltage gradually increases. When the arc voltage is greater than or equal to the voltage value of a certain point on the cd line, the current jumps to the ae line for combustion and enters the next cycle. The location selection of points a and d in the figure is the key point, the voltage value of point a is the lower limit of voltage, and the voltage value of point d is the upper limit of voltage. When the arc voltage is lower than the voltage at point a, the droplet is easily short-circuited with the molten pool and enters the short-circuit transition zone; when the arc voltage is higher than the voltage at point d, it is easy to enter the jet transition zone.

The slope of the selected line ab should be greater than or equal to the slope of the static characteristic of the arc passing through point a, and the slope of line ed should be greater than or equal to the slope of the static characteristic of the arc passing through point d, so as to ensure that the current and voltage changes of the arc are in the subjet flow in the transition zone. The smaller the arc current, the narrower the sub-jet transition area, so the voltage control of point a and the selection of the control point are extremely important. If the voltage value is small, short-circuit transition will easily occur, and if the voltage value is large, large-drop transition will easily occur, which will affect the welding effect; according to the experimental results , This voltage value is about in the range of 14 ~ 19v. When the arc current is large, the sub-jet transition area is wider, so the voltage selection range of point d is wider, and its value is in the range of 20-30v. Even if this point is selected in the jet transition area slightly higher than the sub-jet transition area, it is still It can make most of the pulse current welding process in the sub-jet transition zone.

The above control process is an adaptive control process, which determines the magnitude of the arc current according to the arc voltage value, and automatically controls the arc current and voltage within the sub-jet transition zone.

The present invention will be further described below in conjunction with key issues.

(1) The difference between the voltage values at point a and point d actually determines the allowable arc length fluctuation range. Since the aluminum MIG welding arc works in the rising section of the static characteristics of the arc, as long as the voltage difference at point a and point d is within a certain range , the allowable arc length fluctuation range is not large, which means that the control system has a considerable arc length stability and adaptive control capability. When the allowable arc length fluctuation range is small, the arc current will frequently jump between points a and d, and the frequency of the pulse current will automatically increase.

(2) When the wire feeding speed increases (or decreases), the welding wire melting speed should also increase (or decrease) accordingly. In addition to using the inherent self-regulation function of the sub-jet transition, the control system can also automatically adjust to increase (or decrease) the time of working in the pulse current according to the change of the arc voltage, that is, to adjust the increase (or decrease) Pulse current frequency, thereby increasing (or decreasing) the wire melting rate. In this way, the control system has the ability to automatically adapt to fluctuations and changes in wire feeding speed.

(3) When point a jumps to point d, the current changes along the bcd line. It is hoped to control the welding arc to pass through the sub-jet transition zone. Since the current and voltage on the bc line are positive feedback relationships, the actual current changes quickly . When jumping from point d to point a, jump directly to the constant current characteristic curve of line ae to avoid too long elapsed time in the jet transition zone or the large drop transition zone.

(4) Determination of the position of point a

Scaled by current and voltage coordinates. The current should be less than the critical current for droplet transition, and the selected current should not produce droplet transfer as much as possible. This value is generally below 50A; reversely extend the two lines on the border of the sub-jet transition area in Figure 2. 3. Intersect with the selected current line at two points a and e, so as to determine it. In actual selection, the voltage at point a can be slightly higher than the lower boundary of the sub-jet transition zone, and its value is generally in the range of 14-19v.

(5) Determination of the position of point d

Scaled by current and voltage coordinates. The current should be significantly greater than the critical current for droplet transition, so that the selected current can produce droplet transfer, and this value is generally above 180A; the two lines on the boundary of the sub-jet transition area in Figure 2 are extended forward as shown in Figure 3, The upper curve intersects the selected current line at point d, thereby determining it. In actual selection, the voltage at point d can be slightly higher than the upper boundary of the sub-jet transition zone, and its value is generally in the range of 20-30v.

(6) The voltage at point c should be significantly lower than the voltage at point d, but the currents of the two are the same, so that point c must be in the sub-jet transition zone. The present invention generally takes the voltage at point c to be about 5v lower than the voltage at point d. In Figure 3, there is an iso-melting curve passing near point c, and the slope of line bc should be significantly greater than that of the iso-melting curve, so that point b can be determined.

The present invention can obtain following beneficial effect:

Experiments were carried out using an inverter arc welding power source to verify the sub-jet transition adaptive control scheme for the above-mentioned aluminum and aluminum alloy metal arc welding, and a welding wire with a diameter of 1.6mm was used as an example to illustrate. The main process control parameters are the four physical quantities of base value current on line ae, pulse current on line cd, voltage at point a and voltage at point d. According to the above conditions, Table 1 lists the parameters of several experimental waveforms (Ar shielding gas flow rate 15L/min, dry elongation 16-20mm, welding wire AlMg2/φ1.6), I _ae represents ae line current, I _cd represents cd line current, U _a represents the voltage at point a, and U _d represents the voltage at point d.

Table 1 Process parameter list of aluminum pulse MIG welding adaptive control welding experiment

Tab.1 Welding parameters of Al pulse MIG welding under self-adapting control

Using AlMg2/Φ0.8 and Φ2.4 welding wire can also achieve the same results as the above table.

The characteristics of the sub-jet transition current and voltage value are: the current generally exceeds the critical current of the droplet transition, and the voltage cannot be too high. The critical current for aluminum MIG welding to produce droplet transfer can reach more than 180A, and when the welding current is below 50A, it is not easy to produce droplet transfer. Therefore, in this experiment, the pulse current is selected as 235A, far exceeding the critical current of droplet transition, and the base value current is selected as 30A.

Figure 4 (a), (b) is the time base instantaneous waveform of No.1-2 in Table 1. With the increase of wire feeding speed, the time proportion of pulse current increases, and the average welding current also increases, but the average welding voltage remains basically unchanged. This shows that the adaptive control system will automatically adjust the melting speed to adapt to the change of wire feeding speed, and the arc voltage is controlled within the upper and lower limits of the set voltage. The short-circuit and other unstable states in Figure 4(b) indicate a critical limit state, especially the short-circuit time is very short, and there is almost no rise in short-circuit current, which is a critical state of sub-jet transition, and its control process reflects the The aforementioned sub-jet transition control idea.

Figure 5 (a), (b) is the time base instantaneous waveform of No.3-4 in Table 1. With the increase of the voltage upper limit U _d , the time width of the pulse current increases, and the average welding voltage also increases, but the average welding current remains basically unchanged. This shows that the fluctuation of arc length does not lead to the change of welding current, which has the characteristics of inherent self-regulation. Careful analysis of the time base instantaneous waveform in Figure 5(a) shows that there is a tendency of short circuit at many moments, indicating that it is in the sub-jet transition zone; the unstable state such as short circuit in Figure 5(b) shows a critical limit The state, especially the short-circuit time and almost no short-circuit current rise, is a critical state of sub-jet transition, and its control process also embodies the aforementioned sub-jet transition control idea.

Summarizing the above control results, the sub-jet arc adaptive control of pulsed MIG welding can effectively control the current and voltage parameters of the arc in the sub-jet transition area, and the proper selection of the upper and lower limits of the voltage can make the sub-jet transition efficient. Large adjustment range, automatically adapt to the fluctuation of wire feeding speed, arc length and other conditions.

High-speed camera of MIG welding sub-jet transition adaptive control process:

According to the aforementioned control idea of sub-jet arc adaptive control of MIG welding, the high-speed camera under the process control is carried out.

Figure 6 is a group of high-speed camera pictures corresponding to the period between 20 and 39ms in Figure 8-5(b). A very short circuit occurred between the 2nd frame (21ms) ~ the 3rd frame (22ms) and the 6th frame (25ms) ~ the 7th frame (26ms), between the 9th frame (28ms) ~ the 11th frame (30ms) , the 14th (33ms) ~ 15th (34ms) and the 17th (36ms) ~ 19th (38ms) pulse currents all produced rapid droplet transfer, while other smaller currents and their fluctuations did not A droplet transfer occurs. Figure 6 presents the characteristics of a subjet transition.

Through actual welding, it can be clearly seen that the weld seam is well formed and the cathode atomization area is relatively large; after testing, it can be found that there are no defects such as pores on the weld seam surface. On the basis of a large number of experiments, the present invention conducts experimental research on the proposed sub-jet transition adaptive control idea.

(1) The feasibility of the control idea described is verified, and the adaptive control of sub-jet transition in aluminum and aluminum alloy MIG welding is realized.

(2) Appropriate selection of the upper and lower limits of the control arc voltage is very important to realize the adaptive control of sub-jet transition in aluminum and aluminum alloy MIG welding.

(3) The self-adaptive control system for sub-jet transition of aluminum and aluminum alloy MIG welding has excellent performance, which can effectively and automatically adapt to the fluctuation of wire feeding speed, arc length and other factors.

Claims (9)

1. A sub-jet transition adaptive control method for aluminum and aluminum alloy metal gas shielded welding, characterized in that, comprising the following steps: Determine the five points a, b, c, d and e in the current and voltage coordinates: select the slope of the ab line to be greater than or equal to the slope of the static characteristic of the arc passing through the point a, and the slope of the ed line should be greater than or equal to the arc passing through the point d The slope of the static characteristic, the voltage at point a is 14-19 volts, the voltage at point d is 20-30 volts, the voltage at point c is less than 5 volts at point d, the ae line and cd line are two constant current characteristic curves of the power supply, and the current of ae line should be less than The critical current for generating droplet transfer, and making the selected current not produce droplet transfer, the cd line current should be greater than the critical current for generating droplet transfer, so that the selected current can produce droplet transfer; the slope of bc line should be significantly greater than c The slope of the isomelting curve around the point. Make the arc burn on the ae line, and the arc voltage gradually decreases. When the arc voltage is less than or equal to the voltage at point a, the arc current jumps to point b and increases along the bc line. When it reaches the cd line, the arc current is constant, and the arc is stable on the cd line Combustion, the voltage gradually increases, when the arc voltage is greater than or equal to the voltage value of a certain point on the cd line, the arc current jumps to the ae line to burn, and enters the next cycle. 2. A sub-jet transition adaptive control method for gas shielded welding of aluminum and aluminum alloys according to claim 1, characterized in that the constant current value of the ae line is the base value current, which is less than 50 amperes. 3. A sub-jet transition adaptive control method for gas shielded welding of aluminum and aluminum alloys according to claim 1, characterized in that the constant current value of the ae line is the base value current, which is selected as 30 amperes. 4 . The sub-jet transition adaptive control method for gas shielded welding of aluminum and aluminum alloys according to claim 1 , wherein the constant current value of the cd line is a pulse current, which is greater than 180 amperes. 5 . The sub-jet transition adaptive control method for gas shielded welding of aluminum and aluminum alloys according to claim 1 , wherein the constant current value of the cd line is a pulse current, which is selected as 235 amperes. 6. The sub-jet transition adaptive control method of a kind of aluminum and aluminum alloy gas shielded arc welding according to claim 1, characterized in that, when the arc current frequently jumps between points a and d, The frequency of the pulse current increases automatically. 7. A sub-jet transition adaptive control method for gas shielded welding of aluminum and aluminum alloys according to claim 1, characterized in that the difference between the voltage values at point a and point d determines the allowable arc length Fluctuation range, when the allowable arc length fluctuation range is small, when the arc current frequently jumps between points a and d, the frequency of the pulse current will automatically increase with the jump of the arc current. 8. The sub-jet transition adaptive control method of a kind of aluminum and aluminum alloy gas shielded arc welding according to claim 1, characterized in that, the constant current value of the cd line is a pulse current, and as the arc voltage Changes, automatically adjust to increase or decrease the time of working in the pulse current. 9. The sub-jet transition adaptive control method for gas shielded welding of aluminum and aluminum alloys according to claim 1, characterized in that the diameter of the welding wire used is between Φ0.8 and Φ2.4.

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