KR100782413B1 - Formation method of external characteristic of arc welding power source - Google Patents

Abstract

The present invention mainly adjusts the shape of the load voltage and current and the value of the arc during the formation of the arc of the arc welding power source to repeat the process of the formation and transition of the molten metal drop according to the form of the external characteristics of the power source As the external characteristic formation method, the external characteristic formation method of the arc welding power supply of the present invention observes the instantaneous values of the voltage, current, power, and load resistance in each cycle of the repeated process, and if a decrease in the load resistance is observed, Forming the falling arm of the external characteristic to ensure the formation of the drop in each cycle, and if an increase in the load resistance is observed, forming the rising arm of the external characteristic to ensure the transition of the drop in each cycle do.

Arc welding

Description

Formation method of external characteristic of arc welding power source

1 is a graph showing an amount of change over time of instantaneous values of voltage u, current i, and resistance r with respect to a load.

2 is a graph showing the external characteristics corresponding to these time graphs.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to welding, and more particularly, to an arc welding method using current and voltage pulses generated from a power source manufactured on the basis of an inverter capable of high frequency control.

A pulse arc welding method mainly using molten electrodes is known [RF Patent No. 2 133660, 6MPK B23K9 / 09, V23K9 / 173. Filing date: 1997.7.31. Release date: July 27, 1999 Bul. No. 32]. In this document, the length of the arc distance is automatically adjusted by changing the welding current pulse parameter according to the arc voltage during the execution, and the current parameter is changed by inputting the energy required to melt the drop, and the melting of the drop is the arc It starts from the moment of break-off due to a voltage burst in space.

The main drawback of the method is that the quality of the weld is low, because a short circuit becomes possible the moment the drop breaks off, which leads to a dramatic increase in arc current, and then to the break off of the drop. This is because it causes spattering. In addition, there is no control over the input power at the pre-breakoff phase of the drop (it may be insufficiently heated), and after the drop has broken off and has reached the welded details, insufficient voltage between the electrode and the detail section The arc may be extinguished by a dramatic increase in the voltage of the interval.

A welding method by a short circuit is known [RF Patent No. 2217275, 7MPK V23K9 / 095]. Filing date: 24.09.99. Release date: 27.11.03. Preferred Country: United States, Patent Holder: Lincoln Global, Inc., US]. This document discloses melting a supplied welding wire using a current pulse generated by a power source, and forming a welding cycle consisting of a transfer sector of a short circuit and a melting sector using arc welding. And each current pulse in the period has a specific polarity. The main drawback of this method is similar to the analog method above.

In addition, as a conventional method for the method of the present invention, a current forming method for performing an arc welding process was selected [Patent RF 2210474, 7MPK V23K9 / 06. Filing date: 18.01.2000. Release date: 20.08.2003. Preferred Country: United States, Patent Holder: Lincoln Global, Inc. US]. The document consists of repeated cycles, each cycle comprising an arc welding step after a short circuit step. The period includes a first control mode by current during the short circuit step, and a second control mode by amount of voltage, power, or electrical energy during the welding step. Also for the execution of this process a pulse sequence is generated which forms an adjustable signal curve during the above mentioned short circuit process.

The main drawback of this conventional method is the low efficiency of the welding process control due to the absence of information on the change in the load resistance value (interval between the electrode and the detail). This lack of information will characterize the progress of the process mentioned. Further, the low efficiency of the welding process control of the present conventional method is also due to the input value adjusting member of the following two kinds of electric powers.

Instantaneous power of the short circuit stage: First, it does not necessarily appear due to the instability of the above mentioned interval values. Secondly, the resistance of the drop increases up to the moment of break-off, which, when the current stabilizes, causes overheating up to the moment of break-off or spattering after break-off.

Average power value of the welding process: The average power value is not determined or maintained at the required level, thus changing the average power makes the heating mode of the welded detail unstable.

In order to solve the problems of the prior art as described above, the present invention is to provide a method for forming the external characteristics of the arc welding power supply with improved welding process control efficiency.

The method for forming an external characteristic of an arc welding power source according to an aspect of the present invention mainly controls the shape of the load voltage and current and the value thereof when the arc is formed, thereby forming a molten metal drop according to the shape of the external characteristic of the power source. Iteratively repeats the process of transition, observes the instantaneous values of voltage, current, power, and load resistance in each cycle of the repeated process, and if a decrease in load resistance is observed, forms a falling arm of the external characteristic. This ensures formation of the drop in each cycle, and when an increase in load resistance is observed, it is achieved by forming a rising arm of the external characteristic to ensure transition of the drop in each cycle.

The falling arm of the external characteristic is formed by changing the voltage and the current to adjust the instantaneous power to the load.

The rising arm of the external characteristic is formed by changing the voltage and the current, and adjusting the instantaneous power to the load.

The calculated value of the instantaneous power is averaged within a specific time interval to determine the average load power, which is maintained at a specific level sufficient sufficient for the heating conditions required for welding.

The average load power is maintained by the simultaneous arrangement of the falling and rising arms of the formed external characteristic.

Simultaneous arrangement of the falling arm and the rising arm of the external characteristics is achieved by adjusting the instantaneous values of the load voltage and current within a predetermined limit.

The method of achieving the technical effect of the present invention is as follows. Conventional methods consist of control of the curve shape and value of the load voltage and current, mainly the arc shape, the formation and transition process of molten metal drops is repeated periodically, and the power supply is characterized by external characteristics. It is configured to flow in accordance with the shape of.

In contrast, in the method of the present invention, instantaneous values of voltage, current, power and load resistance are measured and calculated in each cycle of the repeated process. If a decrease in the load resistance is found, a falling arm of external characteristics is formed, which is formed by changing the voltage and current to form a drop in every cycle to control the instantaneous power to the load. . On the other hand, if an increase in the load resistance is found, an ascending arm of external characteristics is formed, in which the drop transitions in every cycle by changing the voltage and current to control the instantaneous power to the load. Is done. The average power of the load is determined by averaging over the specified time interval against the calculated instantaneous power value. This average power is maintained at a level specified / sufficient for the required welding heating conditions. This is accomplished by simultaneously shifting two arms of the formed external characteristic, since they control these values within the limits set on the instantaneous values of the load voltage and current.

All of the important features of the present invention are a continuation of the following operation.

Measure / calculate instantaneous values of voltage, current, power and load resistance and determine average load power.

If a decrease in load resistance is found, a falling arm of external characteristics is formed, in such a way that a drop is formed in every cycle by changing the voltage and current to control the instantaneous power of the load.

If an increase in the load resistance is found, an ascending arm of external characteristics is formed, in such a way that the drop transitions in every cycle by changing the voltage and current to control the instantaneous power of the load.

The average load power is maintained at the specific level necessary / sufficient to meet the heating conditions of the welding required. Since the instantaneous values of the load voltage and current are controlled within preset limits, this maintenance of average load power is achieved by a method of simultaneously shifting two arms of the external characteristic formed.

It is also believed that these features are novel as a whole and have not been known at all, thus meeting the so-called novelty protection requirements.

The above-mentioned effect is achieved due to the above-described overall characteristics of the present invention. That is, the welding process control efficiency is increased by obtaining / using additional information on load resistance change in each cycle. This increase in welding process control efficiency is due to the fact that the instantaneous power input in the load is adjusted in response to the change in resistance, and in particular the formation and transition of molten metal drop in the short circuit stage is assured. It is also because the average power is adjusted for the stability of the specific heating conditions of the welding process, and in this respect it is believed that the present invention meets the so-called inventive level of protection requirements.

The method for forming external characteristics of the present invention can be applied to an arc welding power source equipped with a rectifier and using a high frequency inverter. Welding can be done manually or automatically, and the arc together with the molten electrode is protected with flux, inert, or active gas. There may or may not be a short circuit mode with a molten metal drop. The voltage and current at the outlet of the inverter are regulated through pulse-length modulation (hereinafter also referred to as PLM) of the AC circuit voltage. Inverter switch control and PLM execution are performed with a controller with a programmable microprocessor.

The external characteristics of the power supply are understood as the dependence of its output voltage on the load current, which is expressed in the form of non-linear resistance in the intervals of electrodes and details that change over time. The external characteristics are as follows.

Static state: A stationary or slow changing state (slow process) of the load that significantly exceeds the duration of the process repeat cycle in drop welding (a few steps).

Dynamic state: The load resistance change time is shorter than the duration of the cycle but is 2-3 times longer than the switch commutation period of the high frequency inverter of the power supply.

Furthermore, there are processes (especially PLM) that occur during the interval, the values of which approach the electrical energy generation period of the high frequency inverter.

1 is a graph showing an amount of change over time of instantaneous values of voltage u, current i, and resistance r with respect to a load. FIG. 2 shows the external characteristics corresponding to these time graphs: A line segment (idle sector at initial light emission of arc), B line segment (main sector), C line segment (specific average power curve for load), D line segment (sector of the pole load DC of the power supply). The F line corresponds to the current amplification for the hot start of the arc and the G line corresponds to the electrode antistick protection current. Line E determines the voltage drop on the supply bus to the electrode. The closed broken curve of numbers 1-7 is a dynamic external characteristic with a point 0 inside, located at curve C, which corresponds to the average power of a specific welding mode.

이다. The instantaneous values of voltage u and current i must be read during the welding process of the division period T to form the external characteristic of the power supply, and the division period T can be divided into the switch commutation period of the high frequency inverter. Or it should be the same as this period. The instantaneous power p _i = i _i * u _i and the load resistance r _i = u _i / i _i are calculated according to the measurement result for the i th section. Based on the instantaneous power values thus obtained, the average power of each cycle period T _c = n * T is calculated (n is the number of divisions in the cycle period), and the formula is

to be.

에 의해 결정된다.Then within the time interval of the number j, and within the duration of t _c = N * T _c (eg N = 10 for 10 cycles), the average power value is a similar formula

Determined by

This is more precisely defined in the process.

The interval change of the load resistance is calculated for all divisions. If dr / dt <0 (decrease in resistance), a descending arm of external characteristics is formed, and if dr / dt> 0 (increase in resistance), a rising arm of external characteristics is formed.

1 shows a time graph of current i, voltage u and resistance r. The characteristic change in FIG. 1 occurs in the case of welding by a short circuit having a corresponding external characteristic (see FIG. 2).

In the interval up to point 1 the arc is burned and the electrode is heated (point 1 corresponds to constants i, u, and r in external properties). In point 1 to point 2, a drop begins to form at the end of the electrode, and the resistance r decreases and the current increases. Here, a descending rock of external character begins to form. In the point 2 to point 3 interval, the drop becomes larger to contact the detail, a short circuit occurs, the current increases, and the load resistance suddenly drops to the resistance of the supply bus. On the external characteristic, the descending rock continues to form. In point 3 to point 4 sectors, the drop causing the short circuit is large (exuded), the resistance decreases, and the current continues to grow to heat the drop. The falling arm of this external characteristic continues to form and the voltage decreases somewhat. At points 4 to 5, a neck is formed at the top of the drop, which becomes thinner and the resistance begins to increase. Point 4 is the boundary point, and after passing through this point, the load resistance starts to increase and becomes dr / dt> 0. The power in the load must now be reduced, otherwise the drop will overheat and sputter before break off. This requires the formation of a rising arm of external character.

The drop breaks off at points 5 through 6, which causes the resistance to rise significantly and the voltage to increase, allowing the arc to continue burning without the drop. At this time, a rising arm of external characteristics is formed. In point 6 to point 7 sectors, a steady state arc mode is burned with minimal current, and the formation of the externally rising lift arm stops and returns to the initial point 7 (1). This process is similarly repeated in the next cycle, and the dynamic part of the external characteristics is formed in the same way in the cycle described.

In order to achieve the required heating of the welded detail and the heating condition stability of the welding mode, a specific average power must be supplied which differs from the changing characteristics of the current and voltage instantaneous values. The specific level is determined by the position of the average power on the C line. To implement this control, the average power value must be determined and, if necessary, the curve shape and current and voltage values must be changed while maintaining the form of dynamic external characteristics. Point 0 located within the dynamic external characteristic should be adjusted to be located on the C line. When the welding mode changes depending on the material and thickness of the welded detail, the electrode diameter, etc., new specific values of the average power and curve C are defined.

Static and dynamic external characteristics are set using controller microprocessor software that drives the core of the high-frequency inverter. By using pulse modulation in accordance with the specified control algorithm, the controller regulates the voltage and current within specific constraints on the minimum and maximum values, taking into account the characteristics of the load resistance change. This provides the required value of instantaneous load power in all sections of the cycle and also provides the required value of average power for the stability of the heating conditions (heat input and heating losses) related to the details to be welded.

Therefore, the control efficiency of the welding process is achieved through the execution of the method of building the external characteristics of the welding power source of the present invention, the method as follows.

-Obtain and use additional information on the load resistance change from the measured instantaneous values of the load voltage and current of all divisions in the repeated process cycle.

-Adjust the power to the load. In other words,

In the case of instantaneous power: it depends on the change in resistance specified during the drop formation and transition (when a short circuit occurs or is absent), which reflects the resulting dynamic external voltage and current relationship.

For average power: Maintain the average value at a certain level to provide stability of the welding process heating conditions (heating input and heating loss). This is achieved by adjusting these values within specific limits on the instantaneous values of the load voltage and current and arranging both arms of the external characteristic simultaneously without changing the shape of the built external characteristic.

The technical effect of the method is to increase the welding process control efficiency. The above effects of the present invention are achieved by obtaining and using additional information about the load resistance change in each cycle of the welding process and by adjusting the power input in the load. Instantaneous power at this power input is determined by external characteristics formed by the change in resistance (in the case of occurrence or absence of a short circuit), and the average power is at a value that ensures stabilization of the specified heating conditions of the welding process. maintain.

Claims (6)

Mainly in the formation of the arc, by adjusting the curve form and the value of the load voltage and current, to form the external characteristics of the arc welding power source to repeat the process of the formation and transition of molten metal drop according to the form of the external characteristics of the power source In the method, Observe the instantaneous values of the voltage, current, power, and load resistance in each cycle of the repeated process, If a decrease in the load resistance is observed, a falling arm of the external characteristic is formed to ensure the formation of the drop in each cycle, And if an increase in the load resistance is observed, forming a rising arm of the external characteristic to ensure transition of the drop in each cycle. The method of claim 1, The falling arm of the external characteristic is formed by changing the voltage and the current, by adjusting the instantaneous power to the load, characterized in that the external characteristic of the arc welding power supply. The method of claim 1, The rising arm of the external characteristic is formed by changing the voltage and the current to adjust the instantaneous power to the load, characterized in that the external characteristic formation method of the arc welding power supply. The method according to claim 2 or 3, The calculated value of the instantaneous power is averaged within a specific time interval to determine the average load power, wherein the average load power is maintained at a specific level sufficient for the heating conditions required for welding. Method of forming external characteristics of the power supply. The method of claim 4, wherein Wherein said average load power is maintained by a simultaneous arrangement of the falling and rising arms of said formed external characteristic. The method of claim 5, And simultaneously arranging the falling and rising arms of the external characteristic is achieved by adjusting the instantaneous values of the load voltage and current within a predetermined limit.

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